The Car
The 2026 Audi RS3 is Audi’s sporty, compact sedan. Turbo charged with 394 horsepower, a sport tuned suspension and a proper enthusiast’s steering wheel, this car is an absolute hoot to drive. But the stereo? It kind of sucks. Especially for our client Paul who has enjoyed a variety of aftermarket audio systems over the years. Which is why he asked us to tackle this Audi RS3 audio upgrade.
I was surprised to see the SONOS badging on the door. Typically in an Audi with “premium” sound we see a Bang & Olufsen or Bose emblem. Audi’s equipped with one of these premium stereos typically have a separate amplifier that is part of the vehicle’s fiber optic network.
Mapping it out
The 1st place I like to start is with a vehicle wiring diagram so I can verify the number of speakers I see in the car and see how they are configured off the factory amplifier. With the vehicle wiring diagram I can confirm exactly how many channels of audio we are working with. The only trouble is because it’s a 2026, we didn’t have any wiring diagrams yet available on ProDemand.
The trouble with the Audi SONOS audio system
The SONOS system in this 2026 Audi RS3 has your typical overprocessed factory premium audio sound. Upon first hearing it I noticed everything is up front. There is zero rear fill. Even if you fade to the rear, there’s nothing going on back there.
It sounds like they were trying to create a front and center sound stage for both the driver and front passenger. Which to me is kind of like all season tires. They’re okay. Nothing like the performance you get in winter with a winter tire or in summer using a summer tire. This audio configuration is passable for most, but disappointing to those with a good ear. And the bass? Quite boomy, disappointingly shallow and all up front. The bass is mostly coming from the front doors even though there is a subwoofer in the trunk. Overall there is no detail or separation. Everything is sort of all smooshed together.
Our client’s biggest disappointment was the utter lack of rear fill. He was looking for a much more immersive and enveloping sound. He describes the SONOS system as though he is listening from far away. As though the music isn’t even in the car with him. That’s a great way to put it. So, how do we tackle this 2026 Audi RS3 audio upgrade?
The factory configuration
Before we can upgrade the audio we first we need to figure out the factory set up. This car has 16 speakers. Most of them reside in the front of the car. In the front doors you’ll find the front mid bass drivers. There is no midrange even though it looks like there is a grille in the front door for some mid range speakers.
And then there are tweeters on the A-pillars along with a mid range in each corner of the dash and a pair of mid’s in the center channel (or it could actually be a dual voice coil midrange – we did not take the grilles off).
In the rear doors there is a set of components with a tiny tweeter. We did not take off the rear door panels, but we suspect this is either a 6.5″ or 5.25″
The signal from these rear door speakers is mixed in a way that creates minimal presence or impact on the driver. I guess Audi assumes most driver’s want a front focused stage. Lastly we have the speakers located on the rear deck. These are tiny 4″ effects speakers. Warning chimes for things like cross traffic detection and blind spot assistance are routed through these rear deck speakers.
The challenge in this Audi RS3 audio upgrade is 3 fold.
- Number one – performance of the existing speakers is being throttled by the SONOS amp. With 16 individual channels, that factory amp is dictating exactly what frequency range gets sent to each speaker and at what timing to create the so-so front focused sound stage.
- Number two – the majority of the speakers in this car are located in the front. In order to create some semblance of balanced rear fill that can keep up with the front, we need either more speakers in the rear OR more speaker surface area.
- Number three – we need to overcome the very shallow, lackluster bass. I know part of this can be cleaned up with a DSP amp, but I anticipated adding an aftermarket subwoofer to provide the truth depth and presence that Paul was accustomed to.
The fix
Ideally I want to grab audio signal before the factory amp, before it’s been processed. If we can grab signal before the amp, while it’s still digital, we can go directly into a high quality aftermarket DSP amp where we’ll have full and total control over the frequency range going to each speaker. The DSP amp also gives us EQ controls and time alignment enabling us to get the desired immersive sound stage.
To tackle the lack of rear fill our client Paul suggested swapping out the rear 4″ speakers to a 6×9. Honestly I found the thought of cutting into the rear shelf of a brand new vehicle a bit repulsive. It’s just not what we do here. Maybe something we did 25 years ago? We’re all about upgrading the sound while retaining the original appearance and aesthetics. I couldn’t envision how we could do this and keep an original appearance, but thankfully our team came up with a great solution.
Audi RS3 Audio Upgrade Key Ingredients
For this Audi RS3 audio upgrade I planned to use the NAV TV Zen V which is a digital pre-amp adapter. I learned from NAV TV we’d have to get the vehicle coded. I didn’t even think that was possible because of the strict SFD2 platform. Audi/VW implemented SFD2 back in 2024. It’s basically a much more secure vehicle operating network.
SFD2 makes it much more difficult for an end user to make changes to their vehicle’s computer. Unlike a Ford using Forscan, you can’t connect to the OBD2 and enable or disable options or change functions. VAG-COM does not work in these vehicles. Any changes made on the SFD2 platform need to be done in an authenticated fashion. NAV TV referred me to NPG Technology for this coding service. They specialize in Matrix headlight activation, but also offer other services.
To power this audio system I planned to use the Helix V Eighteen DSP. This 18-channel amplifier is an absolute powerhouse. It measures just 44 x 255 x 220 mm. That’s about 1.75″tall with a footprint of about 10″ by 8.5″. It has staggered outputs. There are 12 channels rated at 70 watts RMS @ 4 ohm and 6 channels rated at 75 watts RMS @ 4 ohm or 120 watts RMS @ 2 ohm. This is enough channels to cover all existing 16 speakers plus another 2 to power a secondary dual voice coil 2 ohm subwoofer.
For the rear deck speakers I suggested the Sony Mobile ES XS-690es coaxial speakers. We chose the Sony speakers for a couple reasons.
Not only for the larger magnet and overall surface area, but mainly for their tonal characteristics, efficiency and reliability. The Sony 6×9’s feature a soft dome tweeter and aramid fiber cone. These speakers have a warm midrange with a detailed tweeter that is smooth, open and airy.
Coding
I want to tackle the coding session done 1st for a couple reasons. If coding is successful we’ll know immediately because we’ll no longer have audio once completed. I know it sounds weird, but hear me out. We’re basically telling the car it’s equipped with the same type of fiber optic amp that the ZEN V is compatible with – the Bang & Olufsen.
So if we code it and no longer have audio that means it worked because that head unit would be looking for the Bang & Olufsen amp or in our case the NAV TV Zen V in place of the Bang & Olufsen amp. The other reason I want to tackle coding first is to make sure there are no errors on the dash as a result of the coding process. By getting this out of the way 1st we isolate that process from the rest of the work we plan to do. Unfortunately we ran into a snag immediately.
Errors Galore
The actual coding process was very straightforward. NPG shipped us a dongle to connect to the OBD2. They also emailed us a link to a software download with a username and password. We connected the laptop, opened the software, reached out to NPG on Whatsapp and off we went. The process took about 10 minutes. We started the car afterwards and had 3 different errors pop up on the cluster.
- Exit warning malfunction!
- Rear cross traffic assist malfunction!
- Parking aid malfunction!
Not exaggerating. Each error actually has an exclamation point after it on the dash. We let NPG know what we were seeing. They advised they had just successfully coded a 2025 RS3 without errors, but in that car, they did the coding at the very end – after everything else was installed. So we tried a sleep cycle. Next we tried driving the car and then doing another sleep cycle. Eventually we asked NPG to log back in and check it out.
Totally disturbed
The error logged was “Driver assistance systems audio output, Infotainment system, implausible signal. Sound output MIB totally disturbed”. Oh, it was disturbed! Our working theory was that we had just taken away the car’s ability to output any of these warning chimes because we essentially disabled the SONOS amp in preparation of installing the ZEN V and Helix V Eighteen DSP amp. So it kind of made sense to us. We all concluded it was safe to proceed.
Next up, John removed the head unit located behind the glove box. At this point it became apparent what was actually happening.
Missing MOST!
We were all shocked to find this head unit was not equipped with a MOST bus output. No wonder why we had all these errors. We essentially told the car it was equipped with a MOST bus amp. However the cheap head unit Audi put in here isn’t compatible with a MOST bus amplifier.
NPG sent us a picture of what the back of the head unit looked like in the last 2025 Audi RS3 they coded. You can clearly see the MOST bus connection on this one. On our 2026 Audi RS3 that area where a MOST connection would be? It’s capped over. I hoped that metal casing was just a cover. Maybe the MOST connection was hiding underneath it? Nope. This 2026 Audi RS3 was simply not equipped. Upon learning this, NPG Technology stepped up. They kindly and promptly reversed the coding for no additional charge.
What does this mean for the installation?
With the errors gone and factory audio back, we re-grouped. Not being able to use the ZEN V was going to make the installation a LOT more complicated. Number one – it means we HAVE to grab our audio signal after the factory amp after it’s already been processed. Number two – since the factory amp has to stay in line, John has to make a custom T-harness in order to neatly add the V Eighteen DSP. The custom T-harness adds a lot of time to the build. This is because it needs operate in a way that the Helix V Eighteen can be disconnected, while leaving the original system fully in tact.
That’s a lot of soldering
In order to make the T-harness function in a way that the original system remains in tact created a lot of solder connection points. It was a total of 12 solder points per speaker. Across 16 channels, that’s 192 solder connections.
Connection location points
The factory amp is resides in the passenger side rear trunk. It looks like your typical PP-UNI 2.38 style connector. This harness would have been great if we could have taken the factory amp out completely. But since it had to stay in there, John opted to make his own harness. We were already behind schedule with the coding fiasco and he didn’t want to wait another day to receive the PP-UNI 2.38. If we were to do this car again, I would still order one just to cut down slightly on prep time for the T-harness.
The connections were made at 2 different locations. The front tweeters, corner dash midranges and center channel are actually all powered off the head unit. The rear SONOS amp powers the front door speakers, rear door speakers, rear shelf speakers and factory subwoofer.
Toning out – Testing – Identifying
Before John could create and wire up the T-harness he had to identify each speaker wire, polarity, location and function. He tested and toned out each speaker. This is kind of hard to do by yourself so at one point I hopped in and helped him with this process. For anyone looking to do the same upgrade, here are his findings in a nice, neat organized chart.
Testing, identifying and then wiring up the amp was a multi-day task. With 16 channels it’s important to take your time to get it right.
With the amp wiring sorted out, John could shift his focus to the rear 6×9 speakers.
Cutting in the 6×9 speakers
To prep for the new Sony Mobile ES XS-690ES speakers John used a template to mark out the location in the rear deck. This template is included in the box from Sony. He then used a nibbler to start making his cuts.
With the rear openings made, PJ assisted in the process by mounting the rear speakers and applying sound dampening to the rear shelf.
My biggest worry about this car was how they were going to finish out the grilles for the newly added 6×9 speakers. John had a great idea for clean execution and handed that task off to PJ. Using the original grilles as a template, PJ created a new thin plastic grille frame and covered it in simple grille cloth. He secured it in place using tiny magnets. The original speakers and grilles were returned to the client.
I had mixed feelings about the grille cloth. I couldn’t find a grille cloth that was a close match to the existing rear shelf dark gray/charcoal finish. Standard “Gray” grille cloth is too light. And standard “Black” grille cloth felt like too stark in comparison to the original rear deck. However, once it was in place I thought it looked great.
With everything lined up and ready to go, John re-installed the passenger seat and reconnected the battery. Once he started the car and confirmed all systems were functional, he proceeded to connect the amp to power. With the amp powered up, he began the tuning process.
Helix Subwoofer Add-on
Since we didn’t use the NAV TV Zen V, this freed up a little money in the build that could be shifted towards a subwoofer. Our client needed something low profile and dual 2 ohm. We used the Helix IK ES10.1-DVC2. This is a low profile, compact, down-firing enclosure. However in this case our client asked us to mount it vertically so he wouldn’t loose any height for the various equipment he carries around.
This positioning isn’t my favorite. The enclosure definitely creates a greater impact when it’s firing down on the trunk floor, but I also understand our client’s need for functionality. John used two of the higher powered, 2 ohm stable channels on the Helix V Eighteen to power the new sub. The Helix sub added deep and accurate bass. It did a great job filling out the range where the factory subwoofer simply could not perform.
Bass Knob – Bring on the Laser
As with all of our installations, I included a remote bass knob. John and I had different opinions about the location of this knob. Originally he considered surface mounting it above the USB C, below the lip of buttons, in between the Traction Control and Hazard. But surface mounting is not our style. I proposed putting it in place of the 12 volt outlet, but our client offered up the spot right behind it.
Now we had the perfect excuse to try out our new xTool P2S laser cutter. This was John’s 1st project using the new device. He cut his teeth with our Bambu Labs 3D printer learning how to draw in CAD with SHAPR3D. My understanding is learning the 3D software is definitely more challenging than 2D. Still, this is another form of software he has to learn on the fly. Together we figured out the layers, how to import an Audi symbol and gave it a go. He hand filed the edges for a clean fit. The black acrylic matched the rest of the interior finishes perfectly.
Final Result
After extensive tuning on both the input and output side, this Audi RS3 Audio upgrade hit the mark. The Helix V Eighteen allowed us to clean up the audio signal coming from both the factory head unit and SONOS amplifier. Each channel signal was eq’d, levels were appropriately mixed resulting in a clean RTA response.
This vehicle now has proper real fill that is balanced and can compete with what’s happening up front. The audio is tuned for the driver’s listening position creating an immersive experience. There is detail, separation and nuance along with a level of richness and accuracy that was completely absent from the original SONOS system. The bass is no longer boomy and shallow. It is tight and accurate, but not at all overbearing.
The best part is unless you push the passenger seat all the way back or take a closer look at the upright subwoofer in the trunk, you would never know that anything was altered or changed. We did our best to keep original appearances down to the finer details such as the Audi symbol on the custom fabricated remote bass knob insert. If you’re interested in an audio upgrade for your Audi, check out our shop Sounds Incredible Mobile in Brookfield, CT. We’re happy to help you take your audio system to its full potential.