Termen. . . . this made me laugh

http://termen.free.fr/

Apparently 'termen' means red-clover in Gallic or something - and their group symbolises the spirit of the Celts! They've got a couple of mp3s there on that page for you to 'enjoy.' Hah. They need a theremin.

Charlie, don't laugh too soon...
Actually, the name Theremin does come from Termen. Lev Theremin's ancestors were French Huguenots who fled to Russia. In Russia the name still is recognized as french, and is pronounced Termèn. The instrument Theremin in Russia is called Termènvox, voice of Termèn.
(Information comes from Lydia Kavina, who as you probably know is a relative of Lev Termen.)

And the group doesn't claim they symbolise the spirit of the Celts. They mention the clover reminds one of another clover that symbolises the spirit of the Celts. Which must be the Celtic Spiral.

I doubt it that using a theremin would add much to their music, or would make it more interesting to you.