SD, if you happened to have a spare VP100, it certainly could be tried in back, preferably oriented vertically. Buying one just for that purpose isn't a good idea in my view. The short distance of 4' behind you is marginal for setting up a rear sound field, and speakers of very wide dispersion, such as the QSs, would be advisable at that distance.
Note that actual discrete 6 or 7 channel material isn't necessary to benefit from rear surrounds, since processing such as DPLIIx can be applied to 2 and 5 channel source material to send appropriate back ambience to them.
thanks for your input johnk, the QS8v3 might just be the best solution and yeah, if you notice i mentioned not including matrixing so I knew about it, i also mentioned that i already have a 7.1 system but was going to repurpose the 2 M2v3's i have that currently do channels 6 & 7. but it's sounding like the Q's are gaining momentum and since i have a pair of QS8v3's and know how effective they are, perhaps that just might be the way to go!
again, thanks for the input, great advice as usual and it's given me something to think about.