While it is optimal to have all speakers matched, IMHO it is less important that the surrounds match the front 3 speakers, than that the front 3 match each other. Although I cannot site "chapter" and "verse," on other forums, I have run across a few who have happily used QS series surrounds with fronts and center from other manufacturers. The QS surrounds do such a fantastic job, that I believe it's worth a try.

Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton