Fixed. Good Catch. The QUOTE button captured everything on that one.
I'll keep it brief, because this is the type of stuff folks will pay very good money for, but there are several technical papers and a good book that go into great detail the science behind filters and (most importantly) their application in audio playback, respectively.
Suffice to say, crossover filter selection (better referred to as "building the network") is based on a couple of variables. Once those variables are determined (application, speaker type, pass bands, etc.) the setup is resultant (ie. not inconsequential). DSPs offer several flavors of filter types because the hardware can easily support them, but most playback systems only require a choice few....particularly horn subs.