I finnally managed to sleep a complete day (yesterday) and find some time to put my head on piles of documentation from riocar.org & analyze the dead cd-changer: I now control /dev/empeg_state and fixed the no more "pause instead of play". Also the cd-input of the radio module is balanced you are right (hey where you found the cd-changer schematic!!?): I'm still evaluating if it's better to buy a converter or build one with savaged components from original-but-dead cd-changer.

Apart the noise, evertthing is quite stable and, when I fix the audio path, I can assemble the rear of the machine and finnally focus on redefine the software (the lacking area is the title/author display and some other goodies not very critical).

Having my empeg player back is really cool, I couldn't drive without it.