What Vandersteen sub are you going to use? (2wq or V2W). If you are going with the 2wq I would use a fixed capacator either inside of your preamp or amp. Vandersteen recommends using the fixed capacator inside of your amp once you have determined the proper value with the variable crossover. You should call Vandersteen and see what he has to say. He could probably tell you what you need right over the phone. Good Luck. thestryder