The higher the crossover the more directional frequencies will be sent to the sub. You don't want that. Ideally you don't want anything higher than 80Hz going into the sub. That, of course, means that the L/R/C should be able to go to 80Hz. If they can't you just have to go as low as they'll tolerate.
i get to put the crossover on the subwoofer to 180hz but idk if the speaker can go down to 80hz. I'm sure they can't that's why I'm asking what crs does my speaker can handle should i just leave it at default on the receiver @ 120hz . another guy told me to put to to 140-150hz because something to do with, Lower -3dB Limit: 125Hz, Upper -3dB Limit: 20kHz , Frequency Response 95Hz-22kHz
Regarless wether ur speaker will go down to 80hz or, i think you can try crossing them over around 100hz. the higher u cross the more directional it becomes the sub and i bet it will sound like crap. You have to understand that even when your front cant reach very low, but crossing to a high pass remove alot of low frequencies sent to the front , so your speaker will still benifit from high passing.