I second the recommendation for the XM44.
I've had mine for 4 weeks. My system has never sounded better.
I enjoy the flexibility of the independent slopes. Immediately I noticed that my SCC300 subs integrated well with 24db low pass at 80hz, and 12db high pass to my 1801's. I prefered this sound to the symetrical 24db slopes.
I could not discern the phase problems inherent to using asymetrical slopes.
I think the 2nd order slope for my monitors smoothed out a mid bass problem in my room. So, in a way the XO functioned as an eq in my room.
Good stuff!
I have not decided yet if my 1801's are playing cleaner, but they certainly have not suffered any ill effects. To my ears the XM44 is transparent. I like the stepped switches and the mute position for each filter. This helps when I want to concentrate on tuning my subs, simply switch the monitors off, and vice/versa.
Over all a very flexible peice. As Wayne mentions, upgradability is excellent. I'm looking forward to adding another set of filters and turning this one into a 3 way, if I choose to experiment with fully active monitors and subs. Baffle step boards and notch filters etc. all available. After you own one it easily becomes an indespensible addition to your rig IMO. i know it's a bit early for me to claim, but the the possiblitlies are exciting.
BR,
EP