Suggestions for active crossover setup please.

Thinking about putting together a second 2.1 or 2.2 system using a sub(s), two tower mains and running it with a preamp of some sort into an active crossover sending 50hz and up to an amplifier and on to the mains and letting the sub fill in the bottom. A couple questions...

1. Why isn't this setup more common? It seems like most people just send a full range signal to their mains and add a sub. The thing is, the vast majority of speakers don't do very well below 40 or 50hz so why let them and/or the amplifier struggle?

2. I have looked around a little and it seems like there a not a lot of options for active crossovers that can be used this way. Either they are made for pro audio, or they are designed for actively crossing over each individual driver or they are prohibitively expensive (as in the case of the JL Audio CR-1). So, for those who have a setup such as this, what component(s) are you using?

This is still in the planning phase so I am really open to thoughts and suggestions.