so friend has problem with volume on his audi concert, I know what is problem, and also that there are at least 2 adapters on ebay which should fix this ,  (second one is also here: )
second one is smaller and cheaper so I go for this one.
.... adapter arrived at postbox, so I was curious how it's works. So i take closer look at traces on PCB and realize that mcu is STM32, and is only grabbing SPI from display and send I2C to audio controller (TDA7342), so they recreate complete audio control stack, nice, lets check it how well it works ;).
I made simple arduino sketch to get i2c data on this radio , and here are my observations:
input selector is not working,
changing bass/treble/fade/balance can by set different from what is showed on display, check my github for output from arduino i2c sniffer links to files ,, are from "modul from ebay/programatory.com" and file in link  is output of reprogrammed Motorola MCU which I buy like 3-4years back.
so, what to do? return it and try first one(from ebay) or implemented volume rewrite in my code??
so after while I write few lines of code to fix this, code is on my github 
schematics will be there in few days