Can moving wire location at circuit breaker reduce hum?

Hair dryers, kitchen appliances, dimmers,... can cause this even by using dedicated lines for your system. One easy way to check is heat produced from the transformer when idling or with no signal (check preamp also). Try to relocate and eliminate possible suspects as advised above or get a dc blocker, it works. 

You did the test kind of backwards. :) 

Turn off all breakers but your stereo.  If your hum disappears then start turning breakers on until it re-appears. If it remains even when the only thing on it is your amps then it's most likely a wiring issue.

Thanks, Erik.  I’ll try that.

"Would swapping out the wires that go into the two separate rooms at the breaker make any difference?"

Give it a shot, you have nothing to lose!

Some people would prefer to understand the problem with say. DMM, rather than just throw “solution buccaci” at it, and hoping that they hit it..