Ooh, no sub... In that case, all the low freq will disappear. Of course, if your speakers can't handle below 100Hz and there's no sub, that LF is gone anyway. If you can keep the passive sub, you might be able to cook something up (for example -- passive sub with built-in crossover and a pair of speaker input/output, hook the front left and right to the sub and then on to the speakers, make those two large and everything else small -- I'm guessing it's built for something like this). If not, you'll have a hole below 100Hz however you approach it.

Sorry I can't offer any better news than that...