#1
I have a spare power amp (Peavey PV500) laying around and was wondering if theres i way i can utilize it in my current rig.

Right now my rig is:

Guitar>NS-2>Pedals>Rack>Head>Cab
#3
If your cab is stereo, you could run the output from your rack into the head and into the power amp.
You could also use the effects loop output into the power amp into the cab.

Nether one of those options is particularly useful though.