When talking about seperates, the pre-amp (before amplifier) does all the processing, decoding, etc.. The amplifier just takes the signal fed to it by the pre-amp and provides the power or amplification to the speakers.
In a receiver or AVR, everything is in one unit. So your Elite does the processing and also has the amplifier. You can also use an AVR as a pre-amp for certain channels by hooking up the "pre-outs" on the AVR to a seperate amplifier. You may or may not notice any difference, depending on your listening habits, rooms size, etc.
So in your case you would hook up RCA ended cables to your left and right "pre-out" speakers jacks to the left and right "line in" jacks on the amps you purchase. This way th AVR's amps for the left/right channels are not used.
You can't use a pre-amp alone with no amp. There would be no power. There is no reason to assume your Elite can't handle the 80's alone as it has a beefy amplifier section, but it does not hurt to try both configurations to see what you think.
