Most consumers aren't interested and/or are not capable of setting up a true bi-amped system, so most consumer systems are all in one... the speaker contains the amp and active electronics or sometimes there's a seperate box designed to work with the speakers. Several companies make these.
If you're looking to DIY your own, look at RANE, Behringer, or other pro audio electronic xovers.
Also, be aware that you will need to bypass the passive xovers in the speakers and possibly buy external amps to make this work. A RTA would be useful as well.