I still think QS8s for surrounds and M2s for rears is pretty close to optimal. If the rears have to be very close to the seating position then that would be an argument for using 4 QS8s instead of a QS8/M2 mix.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8