I have until now been only running with two channels playing through a 2-channel amp. I'm about to add a second 2-channel amp and speakers, to give me 4-channel working.

Any ideas on earthing this second amp? Where do I ground the empeg RCA ground leads - the same point as the first amp, or at the earth of the new amp? If the second case applies, should I have a common ground with the first amp?