Active filter for B&W matrix 800

Hello everyone,
I own a great pair of B&W matrix 800's and have read and found that the best way to get everything out of them is to take out the passive filter from the bass, and biamp the speakers with active filtering on the bass.
Krell made the KBX especially for this but it is either unfindable or super expensive...
Anyone has experience with making these speakers active with a "normal" and "affordable" active filter, which brand, model would you recommend?