I moved the M80 around 4-5 feet away from the EP600 and it still hums. I removed the ground screw and the hum went down dramatically, but it still has a faint hum. Although it is much better, it won't go into standby mode. So, I still consider this problem unresolved.

One thing I did notice is if I turn the sub crossover to 40, it goes away completely. However this solution is useless since I want to keep the sub's crossover on bypass.

Still looking for ideas I guess.

Shag