concerning the file: its name is asound.conf . I don't remember exactly where it was saved. I guess it was /etc/vendor or /etc/vendor/sound . Unfortunately I don't have a cusp device installed anymore in my car to check its exact location. But a folder names vendor was involved.
Check with a root explorer the exact location and then just move the file into a backup folder of your own, so that the file does not exist anymore in the vendor folder or subfolder. This way, android takes a default audio configuration instead of the faulty config edited by cusp. This is also a solution to install 3rd party equilizers like ViPER4Android on that device. With the bad file installed, Viper cannot be activated on these devices.
This unit is connected directly thru my stock amplifier and I don't see any line out on the device itself.
Usually these devices are deliverd with an adapter suited for your car harness. If they did not change their pcb, you have on the back of the device a black 18pin connector with an installed fuse and a second narrow white connector in the middle . (check my uploaded picture)
I don't know exactly how your device is connected to your stock amplifier(with stock amp you mean the one that came oem with the car, right?).
May be you can check this: if your sound wires use the black connector (this way each speaker has its own 2 wires), then you are using the integrated amp from cusp. In this case, you usually need a high low adapter to send an adapted audio signal to your stock amp unless your amp can receive high audio signals. Additional infos could help here, what type of amp, car aso...
The other white narrow connector, connects to an adapter with many RCA Cinch connectors. Among these connectors you get 2 rca conectors for Line level out for the right and the left signal and a separate one for a subwoofer.
The reason why you should test these line outs is to narrow down the problem. If the integrated Amp is faulty, the sound on the line outs should be ok because they don't go thourgh the amp circuit.
If the sound is also bad on the line out then you got a deeper problem on the codec or audio switching circuit.
1=Adapter with line in and out for audio and video.
2=Front left and front right rca line outs
3=Black connector for onboard amplified sound out, directly to speakers.
4=Car dependent harness