You could do it with separate amps powering them, tho Im not too sure how it would really sound. Part of me thinks it might actually hit the perfect combination, but the other part of me thinks it will not, you would have 2 separate sounds comming from the woofers, one trying to hit a certain frequency, the other trying to hit another and I think it might clash.

Just because they are set to different frequencies, doesn't mean they will only hit on those frequencies. They will still hit the same time just with a different tone because they are setup different, might sound really crappy... Just have to try it, or if your lucky someone has tried before but that's doubtful. Most just stick with setting up one or duals together and leaving it be.