I read in Widescreen Review that some of their reviewers run their pre/pro outputs to crossovers that split them to separate amps for their main speakers and a dedicated sub for each of those channels. That is, a sub for the two front mains and two rear surrounds, but not the center channels. These don't necessarily have to be monster subs. But the sub that is wired from the LFE output of the pre/pro is generally the "big" sub.
You could split the signal after the pre/pro and send them to separate amps with built-in crossovers before they go to the mains and their accompanying subs. But the better way would probably be to run the pre/pro signal to a powered sub for each channel that had an adjustable high and low pass filter. Then the high pass signal would go to the main speaker's amplifier and the low pass signal would go to each sub. Either way, you would set all speakers to "large" so a full range signal is passed to all main channel outputs.
People who have experienced this setup say it improves imaging and refines the bass and LFE reproduction. But like most folks I don't have the cash OR room for such a setup, and therefore only use one sub wired from my LFE out.
Avguygeorge is right. I'd think you'd need an exceedingly large room for this, but the Widescreen Review systems were all diagrammed and seemed to fit in "normal" sized spaces.