the 6 ohm load will not be a problem for a denon, or an onkyo. i have the onkyo 701(100watts per channel), and it powers my QS8's with no hesitation. i believe the real stress comes in when you drop to a 4 ohm load, like with the M80 towers. but other than that, you should be fine.
and although side placement is considered the 'ideal' place for the surrounds, there is no probs with putting in the rear.. several people on the board have their QS4's and QS8's mounted on the rear wall, and are very happy with the result.
bigjohn
