Eddie, although you refer to "rears", keep in mind that in a 5.1 setup these are actually side surrounds, and in theory should be directly to the side of the listening position. Nevertheless, in the absence of back speakers(as would be present in 7.1)it's suggested that they be positioned slightly(maybe 2')farther back than directly to the side, to lend a little more back effect.
For the best reproduction of the ambience in music using DPLII, etc. and good performance on discretely placed musicians or other sounds when playing 5-channel material the QS4s should fit your situation very well. They should be mounted on the back wall(facing frontward)about 3' above ear level and separated as widely as possible, nearly to the left wall and a similar distance to the right.
