Who says they aren't popular? The reason you don't see many is once you have one in your system--You are not going to give it up! Occassionaly you will see one and they sell fast. For me the greatest single improvement was going from a passive bi-amp system to an electronically XO system. There are some caveats: With 3-way electronically XO's, (ie tweeter, mid & bass), there is a much higher probability of blowing tweeters (in my 3-way system I have blown 2 sets of tweeters in the last 5 years--and both times I did something stupid); then there's the hassle of 3 amps and the clutter of that much more cables and wires. But the sound makes it worth it IMHO. Marchand has wonderful kits for electronic XO's. You do have to set levels but this also gives you the flexibility to make it sound the way YOU like it. The other beautiful thing, is it frees up your tube amp to do the things they do best and allows you to use a solid state amp to do the grunt work of bass. And one more thing: If you are building your own speakers, designing a passive cross-over is extremely difficult. You can buy software or have someone do it for you (recommended if you must go passive) but by the time you buy first rate components, you probably could have bought an electronic XO and I think the electronic XO will sound better!
