How far apart generally should the QS-8 surrounds be, and how high off the ground? I'm having them rear-wall mounted. There will be a rather large 3 person couch either against the wall or a couple of feet from it. The t.v. will be on the opposite wall about 17 feet away.

My ceilings are about 9 feet high.

I'll take a stab at this since I am in a similar situation with my counch along the back wall and rear mounting the speakers. The general consensus around here is to have the surrounds at a height about 6 feet off of the ground (3 feet above listener's ears). However, you don't want them right up against the ceiling either, but with 9 foot ceilings, you shouldn't need to worry about that. As for width apart, I have heard 2 different models of thought. One is to have them in line with your front speakers, and the other is (if you are sitting on the back wall, and have your QS-8's rear wall mounted) to put them just a little bit wider to create a larger sound field.

Most of this advice came right from Alan when I asked the same question. Just remember that the QS-8s are great speakers and are very forgiving. Of course, if you can move your seating a couple of feet away from the back wall, that would be best, but I can't do that myself.

Saint, here is a picture of what a friend did to his basement HT with the QS8s rear and side mounted.
His setup sounds very seamless so the picture speaks more than words.

Jordan, I assume that you're speaking of the surrounds in a 5.1 rather than 7.1 setup. If so, keep in mind that the QS8s will still be "side surrounds" even though they're mounted on the back wall. As such they should be about 6' high and widely separated, say to about 1' from the side walls(or where the side walls would be).