Sub calibration can be complicated.
If you really feel like geeking out on it, here's a quite lengthy
Subwoofer Setup Guide posted on the AV123 forum that you may find useful. I can't vouch for its effectiveness though. I've been too lazy.. uh.. I mean busy to try it, but other people seem to think its pretty good.
For the quick, dirty, and lazy man approach: grab a THX certified DVD and run the frequency sweep, sub calibration test in the THX optimizer included in the extras. This was suggested to me by Jason J in this
thread and it worked very well for me. Fast, simple, and effective.
Regarding your crossovers, they seem reasonable given your speakers. I'd suggest trying a uniform 80Hz all around and see if that sounds better or worse than your current settings. I think the best way to get it right is just to experiment for awhile until you find what sounds best.
Anyway, good luck with it and have fun! :p