X Over Points
You could work with a 100 Hz. Low Pass Filter,
a single 100 Hz. sound wave is like 3.44 meter, so, You would probably not feel any difference from the direct sound from the speakers and the reflected sound from the walls. So, it´s better to obtain the freq´s thet the speaker can handle pure and direct to the listener, and let the subwoofer work the other part.
Remember that the low freq´s will be cancelled ( most of the time, and depending the distance between sources ) in the center, Your position...
So, it´s better to have just one source for the low freq´s.
Yoo could even try the LPF @ 120 Hz, and hear what happens, remember that You are the one there, so dont be affraid to do some research, and a lot of experiments.