I can't read all of this but the BA6209 is a motor driver chip not related to audio output at all. The CD4066 is a very common IC in many decks and equalizers and they blow out with regularity. Of course they are CMOS so that may be why. In my repair of units I put signals in like a 1 KHz -10dB sine wave and follow the path to where it stops. I use a scope for this. It becomes pretty obvious after a time where the problem will be.