I definitely appreciate what your goal is here. I've had the type of setup you're aiming at for quite a while. What I suggest is to use equipment that is designed to accomplish your goal with the best results.
So, a couple options.
You've mentioned the quality of the phono stage more than...
OK, you want one or two good sealed subs. There are several to choose from, but they will be from internet direct companies that specialize in subs. You'll never really get what you want from a Klipsch sub. Some main brands to select from, SVS, Seaton, Rythmik and PowerSound. Do you have a...
There are still better options. Running a sub off a speaker level signal is never ideal. Are you open to exploring any of them?
BTW, I've been doing exactly what you're aiming at for almost ten years...
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What are your source materials?
What model is your music preamp?
This really isn’t the ideal way to do it. Running full range to the speakers defeats half the benefit of using a subwoofer. There are some options.
...and, what are your speakers and amp?