No, I have not attempted a Continuum/theremin duet. In order to be successful, I think you would have to choose a sound for the Continuum that is as far away as possible from the sound of the theremin otherwise the two instruments would encroach on one another’s sonic territory and step all over each other. This is what often happens when two or more theremins play together….lots of fun, very novel, very cool, but musically unsatisfying IMNSHO.
Precision theremin does not usually do well in ensemble playing, and it really only shines as a solo instrument.
As OT has pointed out, it’s a one trick pony and when you got two o’ them ole nags both trying to pull off the same ole trick at the same time, you’re gonna have problems.