I've tried QS8, QS10, M3, M5, two different pairs of Sonys and Totem Dreamcatchers for rears. I could never hear a difference in 7.1 vs. 5.1 so I'm sticking with 5.1.

I'm in a 4,200 cu.ft. space. The fronts and center are 13' and 14' away from my MLP, the sides are 11' and the rears we're 10'.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated