Thanks, @deep_333. Since your post yesterday, I've actually spent a few hours reading about the F8. It looks like a neat sub and offers some appealing controls (not all of which I understand). A few comments have called it "niche," and there aren't many reviews of it, but I like what I've read and it's clear that Rythmik has a superb reputation. And my system might indeed be exactly that niche. At 65 lbs, it's on the edge of what I can comfortably deal with, which is a consideration for me. Perhaps I'll wait to hear what my ortho says about my knee next week....
I will also take a look at the KEFs. For the moment, I'm enjoying the process of opening up my options, learning about different companies, and even exploring dsp and bass management. At some point, though, I'll just have to take the leap... I remain appreciative of everyone's help!