Hi twelly,
1. The Epic 80 system, or the same system with M60's instead of M80's, are good choices for your room size. For the fronts to sound their best, you will need to be able to separate them at least 10' apart, and sit at least 10 - 12' away. They need some space to really open up and sound their best.
2. If you want good HT movie performance, you will definitely want a subwoofer. I just got an SVS PB2+ for my 5500 cu. ft. room and it sounds great with my M60/VP150/QS8 setup. I'll bet the SVS 20-39 PC+ (cylinder) or PB2-ISD (box) would match your room quite well.
3. Your Denon will be able to drive the M80's but if you push them hard you might trip your receiver into protect mode. Generally, the M60's are recommended for use with receivers, and the M80's are recommended for use with separates.
4. I tried my rear QS8 on the wall for a few days before I moved it up to a ceiling mount to match the height of the side QS8's. The QS8's come with 2 large rounded rubber feet that can be placed on the bottom corners on the back of the speaker. The wall bracket causes the top of the QS8 to sit about 3/4" from the wall, so the rubber feet will bring the bottom of the speaker out from the wall the same distance. I didn't experience any rattling while I had mine on the wall. Since these QS8's have four drivers in them, they are fairly heavy, and should remain perfectly still on your wall. I would be more worried about your SVS sub causing the QS8's to move slightly. ;-)
5. Typically you can just get some decent 12 - 14 guage speaker wire and get good results. I've had good success with the Home Depot stuff that is on the big spools that can be purchased by the foot.
Jason
