5.1 side surrounds are best placed to the side of the listening position as stated by John and Randy.
...preferably a couple feet farther back on the sidewall than the listening position would be advisable
John, that is the first I have heard a few feet back is 'preferable' to directly to the side (and 2'-3' above ear level when seated), even for QS8's.
Dolby surround speaker placement recommendation As stated, a case for M22's over QS8's, would only possibly be for back (7.1) speaker placement if you back wall is very far back and you do not want to ceiling mount QS8's a few feet behind the listening position. (maybe 3'-7' back, depending on your room). I had this exact discussion over many posts because my back is 16' behind my listening position. For my back 7.1 speakers, I ultimately decided on ceiling mounting QS8's 5'-7' behind the listening position.*
Much discussion has been done about direct firing vs. radiant firing (QS8) for 5.1 sides. The overwhelming conclusion is most find the radiant firing QS8 to be much more enveloping. The direct firing speakers sound like they are coming from two distinct points, instead of dispersed all around you.
* (My speakers will arrive in 5 days. I will experiment with exactly how far back on the ceiling to mount the 7.1 backs)
EDIT: I type too slow (or think too slow;o). Alan Lloft says 2" is fine for the Q's, but tilting them to give a little more space, is even better. So, yes, 5" clearance for top of QS8's is very good. When people use the Axiom FMB ceiling mount brackets, as many do, they leave about 2" top clearance, so 5" is even better.
What are your room dimensions?
Dist of list. pos. to front speakers?
Dist of list. pos. to back wall?
Dist of list. pos. to each side speaker?
