Your setup sounds the same as mine. I bought an epic 80/500 setup and a denon 3808 for my first ht purchase back in november. MY couch is also against the rear wall.

See the pics in this thread:
http://www.axiomaudio.com/boards/ubbthreads.php?ubb=showflat&Number=189940&fpart=1

My QS8's sound fine on the back wall- and my couch is only a few inches from the back wall.

You will have no problem with the denon 3808 and those speakers.

oh yeah, my QS8's are a little less than 6' from the ground

-David