It would degrade the sound to a greater or lesser degree. I usually use 2 REL Stadium subs that I start to roll off at 25Hz and run my main speakers full range. They do not have as extended a bottom end as yours does so yours should do even better. If you are using line level signal sent to speakers and subs separately then a really good passive filter in the signal line would be the way to go. I also have older Hsu subs and have both passive and active boxes for them. When I use them with my main speakers I do not run the main signal through them. They are fine for HT use but can be heard in music reproduction. IF your sub has good controls, assuming it is powered, then you should be able to get good results without attenuation of the main speakers.
High Pass filter subwoofer integration
Currently using a subwoofer with my two speakers that go down to 25hz. The variable low pass on my subwoofer is 40 Hz-120 Hz. I am thinking of going with a high pass filter to relieve the speakers of the very low end and to get a better integration. HSU makes a high pass filter but I am concerned that It might degrade the sound. Any thoughts would be helpful. My room is not large, about 12x15 with 8 ft ceilings.