My rooms is the same size as yours (within a foot or so each way). I have m80's vp150, 2 QS8's and an EP500. I also have my TV against the long wall and my couch against the opposite wall. I was unable to place my QS8's on the side walls because it is open on one side (into the kitchen) and there is a brick fireplace on the other. As a result, I mounted my QS8's on the back wall, separated almost as far as possible and about 6 feet off the ground. They are mounted flush to the wall with the supplied T brackets.
The QS8's sound amazing the way they are, an indicator that they are very forgiving for placement. Before I purchased my axioms I auditioned a similar setup at someones house that I met on the boards. They had the QS8's on stands at the side of the couch. In my opinion, the QS8's sound better up higher on the back wall than they did on the sides mounted on stands.
Here is a picture of my surrounds: Please forgive the poor quality, the picture was taken with my iPhone.