OK, I'm not an expert in ICE but I have some experience in P.A systems and I believe they work the same way too.

A crossover is also known as a frequency divider.
Normally it is installed like this in a P.A. system :

Mixer output --> EQ --> Compressor --> Crossover --> Amplifire --> Speakers.

A crossover/frequency divider separates the low, mid, and high frequency before it goes into the low (bass) amp, mid amp, and high (treble) amp.

Then only the low amp would be connected to the woofer, while the mid/high amp connected to the tweeters.