Active Crossovers--Who knows about them?

Hi, I'm considering biamping my Vandersteens with tubes on top and ss on the bottom. However, I understand that I'll need a good active crossover to do it right. What are the considerations here? What are the ramnifications for the sound? Can someone recommend a good active crossover?
The choice is very limited. I know Rane (Linkwitz-Riley 24 db/octave, +- $400 ?), Madisound (Idem), Bryston (6, 12 or 18 db/octave, +-$1000, Marchand XM-6 (L-R 24 db/octave, +-$800 ?).
Marchand makes a good unit. That is a true deal for the kit and you really can't go to wrong. I built and own one which I still use. DBX makes a nice unit called 234 (I think and it very similiar to the Marchnd 24db/octave and it a bargain if you can find one but my suspicions are it has been discontinued. The best in my opinion is the Audio Control Richter Scale which introduces low end equalization and allows for the most adjustment. I own one and swear by it.