i use to use QS8's for my surround rears but found that because the listening position was almost 15' away/behind that i had to change them out and go to M2v3 on-wall speakers in order to really make it work right.
that's not a knock at the QS8v3's either. it's an issue of how they work and the hugh distance from the listening position. for me, to get channels 6 & 7 to work like i feel they should, i went with the M2v3 on-wall speakers.
i went with the on-wall because we didn't want the speakers to stick out farther than the QS8's did so i decided to try the on-wall M2's and they worked out great.
they give me enough meaningful volume to work nicely into a 7 channel surround atmosphere that works and works well. i get all the nice highs and midrange from them. also i know that you don't get the LF out of the on-wall but that's what crossovers and subs are for!
i had the QS8's for about 6 months before switching them out with the M2's. i've now had the M2's for about 3 months and this is what i needed. i'd say if i was inside the 10' mark say closer to 8', no question, the Q's would be there but, at 10' and > you need direct radiating speakers...at least to me.
good luck, keep us posted whatever you choose to do.