Was your issue the LPF, or from the XO?
XO was too high for the sub and center. Dialogue was super boomy. Both were set too high.
Lpf in the sub is another fun thing in my office/den setup. I use the sub for the tv system that is 5.1, but the same sub is used for my PC which is 2.1 and has a totally different xo than the main system. It works very well, but introducing the center in the main system made a new problem. Easy enough to fix, but it was irritating.