Dan
I have one of these AV amps and whilst quite old still gives very good SQ (but have not had in a system for a while now). I believe there is a factory reset option somewhere. I did find there were some settings which resulted in no sound from either the A or B speaker outputs. Generally, from memory, simply using stereo mode and Direct Pass resulted in defeating weird AV settings.
Here is a copy of the
instruction manual in case you don't have it. Good luck. Hope you don't have to have it sent for repair as it may simply not be economic.