I had to do it. It took a long time before I got it right, then I had to work hard on getting the OpenTheremin to cooperate, but it happened in the end.
It's not perfect, but I'm satisfied with this first attempt to do a mix with 2 different theremins.
For this video I used my Moog Etherwave Standard, and the OpenTheremin v4. I also used the karaoke track for the music as found on Youtube.