Oh, this section is even duller than the Amps one. If you can't figure out crossovers, then I'm sorry, there's no helping you.....

Crossovers found within loudspeakers are called 'Passive' but you'll be using 'Active'.

Active crossovers are further devices inserted between the desk output and the amplifiers, splitting the spectrum into it's component parts, allowing separate amp/driver combinations for sub, bass, mid etc.

The main advantage of active crossovers is that the crossover's output is independent of the impedance presented to it. This means that active crossovers can be swapped between speaker / amp systems, whereas passive crossovers are often designed for one specific driver system. 
Output independant of output's impedance charecteristics, so can be moved between loudspeaker systems