Hi Chris,
I agree with Mssrs. Bellemare and K.
Try to find a way to make the QS8's work in your room; they are exceptional, and might be a good first step.
I don't think you'd have trouble with your Yamaha. If you did, you could just add a stereo amp and use its pre-outs.
Excellent observation about wall treatment, particularly on the right side. I'll bet you would notice a very significant overall improvement simply by hanging a rug or something on that short wall next to the right speaker.
I have not heard your Paradigms, but they are well-respected and - if you are happy - you might be better served with other kinds of upgrades. I think that getting M80's and a VP180 would probably be an "upgrade", but I don't know that such a purchase would present good value for you.
Your sub seems fairly small for such a large room. That room looks like it would accommodate a projector and screen nicely.
I'd get (and properly position) the QS8's, use the mini-monitors for rear speakers (i.e. go to 7.1) and think of upgrading the sub rather than replacing the L/C/R.
