I've had the 990 for a few years and got a pair of B&W 804S and an HTM3S center a couple moths later. I tried different crossover settings at that time, and found that having it set at 40HZ for the 804S and 60Hz for the HTM3S was best, so everything lower than that would be sent to the Sub (along with LFE). If I changed the 804S crossover to 60 or 80Hz, they didn't sound as "full", so 40Hz was best. The I'm using DS6 bi-polar surrounds (which is part of the old 600-series) and have their crossover set to 80Hz.

So with those settings, everything below 40Hz for the fronts, 60Hz for the center, and 80Hz for the surround is sent to the sub.