Hey Rage... welcome to the forums!
Just to add a bit to Graeme's "already good" answer....
The ".1" channel, is the Low Frequency Effects channel, of LFE. It's a mono signal so there's really no point in a receiver having 7.2 output. What some receivers DO offer is two subwoofer output jacks in case someone wants to run two subs.... but both jacks are carrying the same signal. Many subs offer a pass-though output anyway so you can daisy chain two subs and, barring all the other options, you can just use a Y splitter from the receiver's sub output.
Many here have found that adding the two extra speakers for 7.1 hasn't added a whole lot to the experience...(possibly because the Axiom QS4 and QS8 speakers diffuse the surround information so well already). The listening room might be the biggest factor (is there substantial room behind the listening room, or is there a couch up against the wall so the rear speakers are just over your head anyway?).
Denon seems to be the receiver of choice for driving M80s. If you have a particularly large room or like it really loud, you can always use a receiver's pre-amp "outs' to add another amp. Even a high power two channel amp to drive your front speakers would take the load off the receiver for the highest demand channels and the lowest impedance speakers...
