Hello everyone, I'm having some sound problems with a car I just purchased. There is no sound coming out of any speakers. I have replaced the amp with another factory amp (although it was used) and had the amp recoded to the car. The MMI seems to work fine, as all the buttons work. I can switch to AM / FM and CD changer just fine. However, when a CD is in, it doesn't play. It loads fine and I can select a track, but it never plays. I had the car scanned and the CD changer gives a fault, but would that really effect any of the other components like the radio or Bluetooth? I also have the Tune 2 Air Bluetooth adapter in my car, and it pics up my phone fine, even knows when I'm calling out or getting a call. But obviously no sound.

2009 A4 Avant
MMI 2G High.
both steering wheel and center volume knob doesn't seem to do anything. It doesn't even go onto mute when I press down on them.
Amp has been replaced with factory used amp and coded to the car.
TOok it to a sound guy and he checked all the cables and speakers and there is definitely power coming from the amp, and speakers are all good he said.

Do I just try to bypass everything with an aftermarket amp and new MMI screen like RS nav? Please help. Let me know if any other information would help.