The search term you're looking for at the car-stereo-gear sites is "Active Crossover".

Sometimes this feature is built in to aftermarket equalizers, although there is such a thing as a dedicated active crossover box.

If the feature is built into your amp, though, why do you want it up front? A crossover is something you generally fiddle with only when you're first setting up the system, and then it doesn't really get changed after that.