>>But in thinking about two M80s AND two 600 subs, I wondered how in the world QS8s could keep up!??!

Remember that driver-wise a QS8 is just an M80 without the woofers... and the woofers only kick in below 200 Hz or so. QS8s seem to have no problem keeping up, although I keep looking at them and shaking my head 'cause they're not very big.

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