The Denons run the M80s with no problems and in a space like yours should be all you need. If you get upgradeitis you can always add a 2 chanel amp to drive the M80s at a later date.
Agreed, My room is just a little larger than this, and my Denon 2809 can achieve earsplitting levels. I think your room(and your ears) will be the limitting factor on how loud you play. One thing you might also consider, Mike, is to use a thick curtain to section off the foyer(on a rail to slide it out of the way when you want) and maybe one either side of the other walkthrough.
I can attest to the fact that the M80s are very detailed even at low volume.
