Hiya Mike,
I suspect that opinions are going to vary.
Spiffnme (Craig) has on several occasions submitted that he did not find substantial value in making that change. I trust his judgement.
My own experience (in room somewhat larger than yours) validates Craig's. Before doing the permanent wiring (which would have been a huge pain) and buying additional Axiom(s), I ran a temporary, inelegant cable to a mis-matched sixth speaker for a while. I simply did not think that the extra, rear channel added much, if anything, to my enjoyment of movies.
Since I have ~10 feet behind my couch, I expected a much greater difference in my case than I would in yours. In the room you describe, I would be very surprised if you got a lot of bang for your buck by adding more speakers.
I do not believe there are ANY discrete 6.1 or 7.1 sources at this time. DTS and DD are 5.1 and the 6th channel is synthesized by your processor. It is also typical (if not absolute) for processors to send the same signal to both the 6th and 7th channels; using more than one speaker back there gives you broader coverage and higher SPL possibilities, but not necessarily different content.
Now, please understand, I like my music in good old Stereo, and respect the opinions of others that have had different experiences.
As to which type of speaker to use, some people have reported tremendous success by using their fancy processors to send DVDA/SACD signals to direct-radiating rear speakers (like a M2 or M22). I like my QS8's so much that I think the only reason to use a monopole speaker in either the surround or rear positions is if you are committed to multi-channel audio. So, some of the answer to your question depends upon your processor, amps and listening habits.
Based on what you've described, If you decided to implement this upgrade, I'd suggest a single QS8 and 6.1.
Personally, I'm saving those WAF points for a HDTV.
I'd love to hear your system some time!
