@andy2, I've been wondering that myself. For those of us who mostly use digital playback I think the ultimate setup will use digital/software crossovers that can be switched to whatever you want. Heck, my 12 year old Velodyne sub has this option. You can choose any slope from 6 to 48db/octave. There is a built in digital equalizer, etc. They aren't the only ones to have done this. DEQX is still around and does everything digitally. I don't think they provide the option for phase correct 6db crossovers right now but I'm pretty sure they could if they wanted to. It's just software.