I had a very similar situation and installed my QS-8 at about 20 degrees back. The QS-8 are truly forgiving of placement (good engineering for surround speakers). At that angle, they sounded just great. Since then, I bought a pair of M80s (those are INCREDIBLE), and I had to move my couch back by about 18 inches, which brough the QS-8 back into the "Dolby recommended" position. I can honestly tell you that I did not sense any improvement (maybe even a slight degradation). So, I don't feel you should worry too much about that and you should definitely keep your back walls for an eventual 7.1.
