Strictly speaking (I don't normally nitpick, but the coffee isn't working today ) given the crossover frequencies it is probably more correct to say that the woofer and midrange are combined on the 50s. I think the crossover between woofers and mid on the M60 is pretty low, around a couple of hundred Hz so on the M60 the 5-1/2" driver carries from a few hundred to a few thousand Hz while on the M50 the 6-1/2s have to cover right up to 2500-3000 Hz.

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