The couch would be up against the wall behind it in the setup with the TV 8 feet away. The room is 18x12, but the 12 part ends up being closer to 8 feet when you factor in the depth of the stand with a couple inches of breathing room as well as a foot or so from the back of the couch against the wall to where your eyes actually are when you sit. With the two QS8's both on the back wall, they would be about 14 feet apart. If the one was on the side wall instead, that would move it further apart another couple of feet to get it onto that wall.
Let me know if you need more details. I'm going nuts trying to figure out how to do all this, although I know I really need to go to bed soon so I'm not falling asleep at work tomorrow.
