From your drawing, it looks like you have a Mk 1. Is this the case?

If so, you should add in the line filter (supplied with the unit) to the power feed to the empeg.

Also, you should have the Small inline RCA grounding cables inserted into the audio output path, at the amp end, with the earth leads attached to the earthing points for the amps (which should be common anyway). Also be sure to check that the amp earthing points are connected to the DC ground if your installation instructions say so - otherwise your amps could start to float above ground when delivering a lot of power (high return current) and cause noise problems due to earth differentials, grounding loops, etc.

One of the few remaining Mk1 owners... #00015