I have a similar situation as you. My couch is a few inches from the back wall and I have a brick fireplace on one side and an opening into the kitchen on the other.
I mounted my QS8's against the back wall with the supplied T-brackets. They are spread out a couple of feet more than my mains and about 6' off the ground. While this is not ideal I find that it sounds very good. I still get surround effects that sound like they are coming from the sides as well as sound effects coming from behind me when both Q's are working to produce a surround effect. They are up high enough that I also get the feeling of things overhead such as helicopters, etc.
Overall I would say that the QS8's are VERY forgiving with placement. You won't have any problems at all.
