I found the sound change problem.

after boot up, if the empeg goes into voltage drop protection, (battery icon comes on) the sound changes. I don't know what setting it goes to but it sounds like the front output is dropped by 6db

I have my front and rear spakers driven from the front output and the sub driven from the rear output. The EQ setting is 4 channel.

hope this helps.

Murray
Go-Wit-Da-Fro