I realise it doesn't include a crossover, but if you set one channel with say everything cut above 100Hz and the other channel with everything cut below 100Hz would it have the same function as one?
Only in the bands you attenuate. You will still have full volume on the bands not attenuated. I actually use one of my filters on my BFD to get a little less midbass and it acts as a higher order crossover in the frequencies I choose along with my receivers sub output crossover. Experiment with it and you will find a sound you like.
If you want a active crossover why not look at making one. This one would be stereo 2 way and only cost a few hundred ... go to http://sound.westhost.com/project09.htm it is no harder to make this than a DIY sub ...
Ted