Thanks Alan ..
So even though I have MK 750 THX up for my front three by using QS8 it would be OK.
I guess what I am saying is, mix and matching MK fronts with QS8's for the rears. Or even THX speakers in the front and non-THX for sides and rears ?
I guess, really I will find out the difference someday as I still want my M80's for my front music channel.

Pioneer sc-1525
M80 HG Cherry