[MTCD Android Head Units General] ttmk2_2011:
Hello all!

Edit: if you're not interested in the Story, and just want the solution, scroll to Chapter Four

This already has been quite the journey, in fact I went way deeper down this rabbit hole than I'd like to admit, so here is the story:

General info:

Car: Audi TT mk2, 2011, has Bose audio and hands free talking, previous stereo was the RNS-E

Headunit: Xtrons PB78ATTRP, PX5

So the problem was/is, the unit only outputs Sound in these apps:

-Radio, A2DP, Phone Calls, CD-Player, Music or Videos that are loaded onto the micro-SD

I contacted the Xtrons support, apart from being very unhelpful and not doing anything, I later got them to send me a new can bus-adapter (will come into play further down).

So because they weren't very helpful, and i really liked the unit, and with basically no alternatives (Xtrons units claim to be plug+play with the Bose systems, which no other manufacturer I came across claimed), I decided I'd try to hunt it down myself.

Chapter one: Updated the unit to the newest Xtrons firmware + MCU, that did nothing. Updated it to lots of different MCUs, didn't do anything either. Installed Hal9k, no change. Different MCU again, no change. Went on many searches on google, and found people with similar/same problems, but no solution. Then came across something entirely different ,but it gave me new ideas.

Chapter two: I reset the unit a few times, back to Xtrons, back to Hal9k, no change, then I came across the factory settings: you can access those in the car settings all the way down, then enter 126. Standard setting for the can bus profile was, I think, 23 AudiA3, A4. Changed it to anything different than that, and voila, sound now works like it should (although the Bose amp is now always on, when the stereo is on, giving out a little white noise). However, a new enemy emerged: now the steering wheel controls, of course, stopped working.

Chapter three: Tried many different settings in the factory-can bus settings, of course, no difference. At this point, I figured the only thing that could be wrong is either the can bus decoder box or the MCU. So I got that new box from Xtrons, and nothing changed. More internet search fopllowed: I found out some MCUs work across different manufacturers, Xtrons being "GS" for example. So I tried some different ones, and found my can bus box, being a "GS", wouldn't speak with those MCUs. At this point, I got sick of it and figured I'd learn to live without steering wheel controls.

Chapter four: a month or two after chapter three (Today), I figured why not give it another try. So I did another google research on people with can bus problems on PX5 and found this Thread.

So i did what he did, and: IT WORKS! (sort of) Now I have sound in all Apps, and working steering wheel controls. The amp is still constantly on and makes white noise when no music is playing, and i cant completely disable the can bus app, only force stop it, resulting in probably having to force stop it if it somehow starts itself or the unit reboots (if it only sleeps it's fine).

So now, I finally know where the dog was buried so to say, I guess to really fix this id need an update for that can bus-app, which probably Xtrons won't provide :(

I hope this helped everyone else with that problem, and I'd appreciate any ideas on how to proceed with that can bus-app

have a good one,