#1
would it be possible to run a preamp into the fx loop or something of my combo and use the power amp and speakers with it?

would that be an effective way to get a different sound out of my amp without having multiple amps

my idea is to run a engl preamp into my carvin bel air(vintage series) to get br00tal metal sounds

would this work or do i need a metal oriented power amp as well to achieve a metal sound?
#2
Guitar -> Preamp Input -> Preamp Output -> Effects Loop Return

You're primarily getting/shaping your tone from the preamp. A tube poweramp (your Carvin Bel Ari) will add balls to your sound. It'll work fine.