preamps????

you can use the power amp from your amphead to power the preamp. or you can use a seperate rackmount power amp like the mesa boogie 2:90 or 50/50. both work. and yes, in reply to your question yes. although i recommend a rackmount poweramp instead of using your amphead's
 
Exactly, I've used a preamp with a head for years, just make sure it has what xenophobe says and rig them up like that, should be fine, in fact I think a lot of people tend to use heads as power amps for reliability issues and because they are easier to replace if they die...