From what I have read, matching the rears or rear surrounds with the fronts and center is not especially critical. I had the JBL SAT20s for rears before I bought the QS8s. The biggest difference that I noticed was the better sound dispersion with the QS8s.

The Rat. M80s, VP-150, QS8s, SVS PC 20-39+, OPPO, Onkyo 703s, Harmony 880 Sony 60" SXRD HDTV