I recently received 4 QS8's. With the sides, I tested them tilted 25º and found the low freq. lost 20Hz per what Audyssey sets. With the wall mount 'T' brackets Audyssey set the x-over at 90Hz, vs. 110Hz tilted. My sides are back to flat against the wall.
What size, specs and mounting location were your old JBLs? My old in-wall 8 1/4" Kevlar woofer sides sounded pretty good before. Now I have the Q's there. I may pop the in-walls back in just before return time, just as a confirmation of improvement. So just curious what you are coming 'from' for your sides.
"In theory, practice and theory are the same. In practice they're not."