External Crossover/Vandersteen Sub

You will gain more by getting a fixed value x over.

What is the difference between the fixed crossover vs using the wx2

The WX-2 is used to find the hi pass filer value that you think sounds best. If you have an amp with an input impedance 50K,you try the 50K setting , the numbers should be on the bottom of the box. When you find what K setting you like order that value hi pass filter from Vandersteen. The WX-2 hinders the quality of sound.

They're four options with the Vandersteen crossover:
1. Use the crossover box as you are now using (lowest fidelity)
2. Use a fixed crossover (which if you read the Vandersteen instructions is what you are suppose to use after you use the WX-2 to make a decision which one.)You purchase these from Vandersteen.
3. Make your own fixed crossover. There was plenty of discussion back about 4 years ago about this. It's not hard and gives you the option to pick the capacitors you like best. As far as I know, Vandersteen uses REL caps(yep, I took one apart!) Some other choices are Hovland, Infinicap and a higher spec Reliable caps.
4. The best option is to get the Model 5/5a crossovers (and now Quatro.) They are right expensive new but can be found from time to time for about $450-$500 used. It is battery biased and offers the most transparent sound. They are available single ended or balanced.
Whatever you do, move on from the WX2!

Thanks for the help