Re: Hooking up a pre amp out to a pre amp in?
Yeah, it's called daisy chaining or slaving. You connect 1 amp's preamp out into the FX loop return on amp 2, NOT the input on the front! While plugged into amp one, that preamp tone will be going to both amp's power section. If they're heads, make sure they're still both plugged into their own cabinets. Don't do it while they're on.
If you have 4 input Marshalls or 4 input Bassmans, you can chain them together by using the input jacks on the front, but only on those kinds of amps.