A poweramp is part of your amp, an amp contains a preamp and a poweramp. If you got that then you'd also need a rack pre.
ok so i think i understand, this is how it would go?

Mesa or Marshall PRE AMP--->peavey power amp---->CAB

am i gettin it?
Any preamp will do, Marshall makes a few, Mesa makes one but its a brute.

Aye, thats right though, you can add a tuner, effects, loopers and switchers and loads more to a rack though.

EDIT: When I say any pre I mean any guitar pre obviously.
i was looking at the rectifier pre but it says its for recording, so is that the one that wont be compatible?