Hello enchong and welcome to Audiocircle! It looks like you have a very fine system. As a ModWright dealer and enthusiast, I've had opportunities to listen extensively to both of these models. The LS 100 is a very versatile and high performing preamp. In addition to its sound quality, it has a headphone amp and the option to add a phono stage or DAC. IMO, the LS 100 is as good or better than any other preamp in its price range. But the 36.5 is on a higher level of performance.
You already have a superb phono stage that works exceptionally well with the LS 36.5. I have heard this combination, too. The 36.5 has better resolution, a bigger soundstage, and lower noise floor than the LS 100. Everything the LS 100 does, the 36.5 does better.
I'm sure you'd be happy with either in your system, but the 36.5 would be a better match for your system if you can swing it. Good luck and good listening!
Scott