Frosti, the back surround speakers in 7.1 setup require some room behind the listening position(say at least 4')for the back surround effect to develop. If you can move the couch forward enough to make 7.1 worthwhile, then the side surrounds should be on the side walls directly to the side of the couch and about 2-3' above ear level. The back surrounds should be on the back wall(facing forward)at the same height and separated to the left and right edges of the couch.
If you remain almost up against the back wall, a 5.1 setup is advisable; the surrounds could either be on the side walls just a few inches from the back wall or on the back wall(again facing forward)just a few inches from the side walls.
