hum Being caused by ??

Check if all components use pin 2 hot and pin 3 ground. I would suspect that one amp deviates from this configuration. Also since purchasing my VAC Renaissance preamp which is truly balanced operation, I find out that my Sony cd player and my Classe amps that utilize balanced connections are really not truly balanced as far as operation so maybe you have one component that is truly balanced with others that only have balanced connectors. The VAC has a switch which changes the grounding for the type of operation ie truly balanced or just balanced connector. If the ground switch is incorrect it can hum and or reduce output.

ok connected the CD player via balanced outputs into main upper range amplifiers,I disconnected all other wires for the bass crossover/amplifier.I used cheater plugs to lift all the AC ground pins I still have the same resulting hum as before? Any suggestions? Thanks

I wasn't talking about lifting the power cord grounds. My preamp has a toggle switch right at the XLR connector to change the grounding arrangement for either "truly differential balanced" or just a plain "balanced" operation. I would suggest you contact the various manufacturers and find out if one component is different in operation, ie simply "balanced" or "differential balanced". You could also have an equipment problem such as a bad solder joint for one of the XLR sockets.

I realize you weren't talking about lifting the AC grounds. My amplifiers have a switch for balanced/RCA input it was on balanced when humming. Just trying to give more information about the problem so others could possibly help me figure out how to solve it. Thanks Justin