You're sub is not very well integrated for that situation... they report a high end of only 200Hz, which is pretty normal for a sub. I don't know how much higher it will play cleanly, but for a 180 XO, you would want your sub to play cleanly up to about 240 to cover the slope of the XO.
You'll need to experiment with lower settings, but be aware that depending on the physical limits of the speakers themselves, you may be pushing their limits with lower XO settings.
By how much, I cannot say.