OK, an amplifier merely takes the line level signal and amplifies it to speaker level.
A pre-amplifier is, at its most basic, simplified level, a volume control. The vast majority of them also switch between sources.
Preamp/processors also decode digital signals from DVDs, CDs, BDRs, etc.
Receivers incorporate amps, a pre-amp, and radio tuners in one unit.
To use a receiver with an amp, the receiver must have preamplifier-outs, aka pre-outs. Hook the inputs of the amp to those pre-outs for the front channels.
To your last question, yes.
