I'd be inclined to drop the 3rd QS8 as it won't a much for you. Also, the 20-39 Plus is a bunch of sub for that room. I use a 20-39 PCi in my 16x22x10 room and I still have quite a bit left over.

Have you called Axiom and /or SVS to discuss your choices? They are terrific on the phone and will give you th eguidance you need for the right choice.