I would definitely talk to Richard Vandersteen. He's a nice guy. I believe the X-2 crossover is a first order 6dB per octave slope. Basically it's one capacitor but the value will vary based on your system.
Looking For Someone To Make A Vandersteen X-2
I’ve read online that it’s possible to make a high pass filter (80 hz, 6 db per) similar to the Vandersteen X-2, but perhaps using a higher grade of capacitor than is offered in the stock X-2. Unfortunately I have no confidence in my ability to pull such a thing off, so was hoping some talented a’goner might be willing to build a set for me. If you’re willing and able, I’d really appreciate hearing from you!