As a Vandy owner, please join us on the Vandy forum -just go to the Vandy website and you'll see a dropdown. There you will get all the info you need.
And, Mr. V. will often chime in.
If you don't want to join, then PM John Rutan (audioconnection). He won't steer you wrong, either.
In any case, you do need a pair of crossovers. They are put in between the preamp and amp. So, you need to know the impedance of your amplifier so that you can order the correct crossover value. (Vandy offers set value crossovers, as well as an adjustable crossover-M5-HP. the set value crossovers are a bit less expensive).
This all assumes you have a separate preamp and amp.
If you have an integrated amp, things get a bit more complicated.- which means either posting on the Vandy Forum or PM'ing Johnny R. for the best advice.
bob
Bob