Let me just join in and (also agree with Alan and) say that the difference between 5.1 and 7.1 (especially with the QS8s or 4s) is prety minimal when the set-up involves a couch right up against the wall.
That said, if the side walls are far apart, it might help to focus the panning effects, especially when coupled with a rear matrixing software liek Dolby Pro Logic IIx.
I have my rear speakers above the couch on the back wall. They would fire right over my head, and probably be heard after their first reflection on the front wall as sound coming from the front... To fix this, I point the speakers straight up. They bounce off the ceiling and hit the listening area more directly. The sound is still quite diffuse and "feels" more like its coming from the rear than the ceiling. I like this set-up, but would be perfectly happy to get rid of them.
At the end of the day, if you're going to buy them no matter what - then have at it -a it certainly wont wreck anything. ai If you're on a budget, think about spending your money elsewhere. There's so little information that gets sent to the speakers anyway that they mostly pull double duty with the side surrounds anyway on most discs...
