Cant Figure Out What's Wrong..

[duct_tape123]

Check for a bad RCA. Get some Y-adapters instead of running one amp from the pass-through of the other amp.

[jmsonoma03]

Nah, both amps the phase is set to 0

i dont think he was talking about the setting on the amp you should double check the connections on wires from amp to subs make sure all pos are to pos and all neg is to neg if you have one backwords you will have less bass easy way to test is to disconnect wires from amp and pop them get a battery from a drill 9- 12 volts and touch wires to bat if speaker pops out its correct if it sucks in its out of phase.