My DDIN has an active crossover in it. I believe all the newer Kenwood units do.
Mine is the Kenwood DNX7140.
You can also pick up an external active crossover such as
Kicker KX2 Active 2-Way Electronic Crossover at Crutchfield.com
The only issue I can see is trying to use a component system instead of getting individual tweeters and 6.5 inch woofers. The reason being that a component system is generally designed by the manufacturer to work with their crossover off of one input whereas the individual speakers would be designed to work on their own and would list the proper power handling and specs.
I had that kind of setup in a previous vehicle and to be honest, it sounded exactly the same as the component system I have now. If you want the control over the individual speakers, though, it would work well as long as you use the proper parts.