Hi John,
No need to apologize. As PJ suggested, the information about the crossover is confusing.
I agree with what you're saying about adjusting the low pass filter on the sub.
As to whether it matters that the main speakers are getting low frequencies they can't reproduce, the usual info opined is that the low frequencies could have a deleterious effect on the bass you do want them to reproduce, though I think that is usually considered more of an issue at higher volumes. And of course, if you weren't using a sub at all, those frequencies would still be going to the main speakers. In my office setup, for example, I have the same situation and don't discern a problem, but it's (almost) never played loud.
Despite PJ's humble protestations, he knows more than most anyone, and it would be worthwhile having him weigh in on this question too, rather than listen to what I've heard others say.
Good luck and enjoy,
Pete