Yeah, the basic Rane is not really meant for subs (and their better models cost a lot more). dbx makes several models that would do the trick, depending upon how low you need the crossover point (I think their standard models go down to 40 Hz). They are fairly inexpensive and good quality. I am using one in my system and it is working well.
Marchand makes a number of models if you know what frequency you want, or you can roll your own if you are tech-savvie. There are a bunch of various kits on the 'net.
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley