I think the big difference is that the QS8s can handle more power and play at higher volumes (or same volume in a larger listening area). Many people (including myself) went with QS8s because it was one less thing to worry about, or because that gave the same driver size on all our speakers, but I don't remember seeing anyone who observed a real difference in sound between the 4s and 8s (except, presumably, at high volumes).


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