Have you listened to your qs8's as rear surrounds yet? I would try that first before ordering another pair.

Swap the m2's(use them as side surrounds) and qs8's then calibrate, and listen to a few movies with Pro Logic IIx. Do the qs8's(as rear surrounds) sound anemic? Are they fuller sounding?

*Michael*
AV123 Refugee - X-LS Encore, X-Voce, X-Omnis, Elt-Dpa's
Denon AVR-591
Magnavox NB500MGX BDP