There's two simple ways of splitting your signal,
1. Use a splitter pedal an A/B or A/B/Y set up lets you plug your bass in to the pedal, then split it in two and run either one channel or the other or both. The benfit of this is you can run the same signal into two differetn amps or effects set ups or as I do one into my bass rig and then one into the B2M and a midi synth, I can then choose to play bass, midi synth or both at a tap of a footswitch. For your set up you could have two amps with two different settings / effects.
2. A crossover. This takes your basic signal and then divides it into frequency bands, you can then send these different frequencies to different places, for example lows to your 15" cabs and highs to your 10" ones. Most good crossovers are adjustable.
I personally would go with option one - you can pick up a good new A/B/Y for about £70 or a second hand one for about £30
Hope this helps answer your question
GD