My brother has the 990/7125. Outlaw's bass management function in the 990 is one of the best I've seen. With the flexibility to set crossovers for each individual channel, its something you should experiment with. In my brothers HT he has each speaker set with different crossovers and it sounds very good.
The key is your individual room acoustics so you would have to listen closely. While 80hz is the well accepted standard, I prefer to set the crossovers as low as I can while still getting good blending (ie. level FR and phase) with the sub.
Settings worth experimenting with would be setting the M60s to 60hz (1/2 octave higher than the 37hz+/- FR on the 60s;
80-100hz on the QS8s; and 60-80hz on the VP150. On the centre I would listen to male voices for naturalness and set the crossover accordingly.
