Earl Geddes is a big proponent of this setup, but for different reasons. He feels you get the best bass response by exiting as many of the room modes as possible, so he has one larger driver to handle the sub 50Hz stuff, runs his mains full range with a natural roll off (12db per octave) around 50Hz and then supplements with 2 or 3 subs covering the 50Hz - 150/200Hz region using high efficiency drivers in a bandpass config.

The trouble with using multiple subs in different frequency ranges is that they can be difficult to integrate. Realistically, a couple of good subs with larger drivers placed properly will get you good clean bass with decent headroom for dynamics.
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Fred

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Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!