Adding a second amp

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?

The grounds of the two pairs are separate, so you can ground them to each amp individually. If the amps are in the same place, commoning power up is probably possible.

Hugo