hey. i just bought a vandersteen 2wq (it's got a built in 300watt amp) and only cost $1,300. (only!...you know what i mean). this sub was supposed to work wonders for my electrostatic speakers (acoustat model IIIs) and it did! ive since learned that lots of people with electrostats love these subs. the crossover is a passive one. it's a simple plug that connects into the end of the preamp interconnect and then that goes into your amp. i think it made a huge difference to the sound. i love it. LOVE it! i hope that helps answer your question. go to audioasylum and post your question there or do a search and you're bound to come up with the answers as well.
good luck
good luck