In essance each driver is powered by a dedicated channel of an amplifer which allows you to control everything in the system individually. You may not be able to adjust it all without a good active eq and a parametric. You typically run a parametric with an active system since you are going with all the bells and wistles anyway.

Finally in this brief reply... you typcially gain an efficiency factor of 4 meaning if you want the output of a 200W setup with a passive crossover you only need 50W in an active system. Don't forget you don't need a lot of power for the higher end of the frequency responce. A tweeter cannot handle 200W, the passive crossover attenuates the power output to the tweeter from the crossover. If you take a look at a set of MB Quart Q line components the crossover lights up red hot from filtering off the power from your amp before it sends a very small portion to the tweeter. Hope this helps.

Thx