Brian,
Wow!! I'm flattered that you would want to perform my "Passacaglia for Theremin and Strings" that I assume you saw up on IMSLP.
This is a piece (a true Passacaglia) written in an obviously Neo-Baroque style with a more modern lush harmonic setting - yet very accessible. But there are a few parts in there that are very difficult - particularly the runs in the middle. I would be willing to simplify this if you do like it and can find a thereminist with decent chops but is fearful of that exposed part - and get you more of a performance score. A good thereminist could play it - however those scalar passages would give any thereminist a run for their money.
I have other things for theremin and strings but they are much more "Boston pops"-like oriented and shorter. Mostly stuff I wrote for myself to practice with (I've only been playing a bit more than a year).
If you are interested, I did up a quick MIDI mockup (not nearly enough dynamic variation) of the piece using a theremin sample set I have to give you a better idea of it should you really be interested. This will let you determine if it's something you want to try and play or not.
https://soundcloud.com/rk53-1/passacaglia-for-theremin-and-strings
In any case - Thanks - You made my day.
Rich