Do you have any tuner cards installed in the unit (AM/FM/XM). Since these are internal to the AADS there are no external factors to have an affect.

What happens when you adjust the balance all the way to the right? Does one speaker get louder or does the room just get quieter?

Since this is happening on all rooms it doesn't sound like an amp issue as each room has dedicated amps and I can't see all the right amps only going bad. This is either the input has gone bad, the source cable has gone bad, or the source output gone bad.

As kgossen has mentioned, what happens if you change the left and right input cables? Does it switch to the other speaker or stay with the same speaker?