I had my x-over at 150Hz for a while, and I thought it had more 3-D sound than at 100Hz. I think there was something going on with the speaker placement: the "mains" are M3Tis in the top corners of the room. Since I put in a parametric equalizer to get reduce room resonances from the sub, I've kept the x-over at 100Hz, because of some stuff to do with the PE I won't go into here, but I'm happy with this too.
I think this "bass localization" thing will make such a subtle difference at these lower frequencies (150 Hz and below) that you won't care unless you're trying to find it. Bass sound sources usually aren't pure, so the overtones will localize the drum or the bass guitar more than the sub tones.
Trust your ears. Assume that if you try hard enough you'll find something wrong with your system. But enjoy the positive.
Good luck,
--Martin
