That's probably perfect for the M3s but might be a bit too low for the QS8s. You're going to have a bit of a "hole" between 80 and 100 Hz when running the QS8s -- that might explain the different sound. In the interests of science, any chance you could set the surround x-over to 100 hz and try the rain in U571 again ?

I know what a pain it is switching speaker interconnects, just finished doing the same thing last night and again today. Banana plugs are looking more attractive every time

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