Good morning everyone

I need to lower the XOVER point on my Epik Valor sub. The lowest setting is 50hz. Im running my speakers full range with sub filling in the bottom. This setting worked well on my Magnepan 1.6s but not with my 3.6s so what to do?
Sell the sub? Perform some minor surgery? Buy a new subwoofer amp plate?
My sub is wired from the speaker binding post. I cannot connect from the then preamp out.
Thanks in advance