Alas, this is a twenty year old product, so there is a limit to how much support we can offer.
It does sound as though you have an A/D or D/A problem.
Because of the age of the unit, you will have trouble finding a local service place. Your best bet is probably Sound Service in Dusseldorf (Germany), but even they may suggest you return it to the US.
The Orville has detachable audio boards – maybe if you placed a deposit, we could send you one to see if it works.
Before you do this, I would suggest that you (or a technologically competent person) try exchanging the two boards, and see if it makes a difference.