Not to hijack the thread, but I have a similar situation. So side walls, just a back wall.
A positive is that a main viewing area is the backwall.

My AVR is capable of 5.1, 6.1 and 7.1. Needless to say, going 7.1 isn;t going to offer anything with this room layout.

Would 6.1 offer some advantage? The distance between the outside "surrounds" would be about 12 ft I would guess

Mark
Pio 94,SB3,BD30,A35,Pio 48AV.Pronto 7000 controlling all. Getting ready for 22s, 150 & QS8s.