Tiger, welcome. You really don't have the option that you're proposing, but you don't need it. If you mean that your QS8 positioning would be about about 20 degrees farther back than directly to the side of the listening position, then that's just about ideal for the side surrounds in a 5.1 setup. They should be a little farther back to lend a little more rear surround effect in the absence of back speakers in a 7.1 setup.
Furthermore, most(all?)receivers don't permit back surrounds to operate when side surrounds are set to None. Even if it could be done, they would be sent different(and wrong)material than what they should be reproducing, and some sound intended for the sides would be lost.
