Recording the theremin straight into my DAW

As stated in the title, I'd like to start recording my theremin and prefer to record direct into my DAW rather than use a mic. I'm new to recording and to DAWs so not sure exactly what I need to do this. Does anyone have any recommendations on what interface would be best for this? I tried recording in a friend's studio, not sure what interface he had, but the theremin produced a lot of noise/buzzing. I'm not sure if it was all the electronics in the small studio space or if the interface was not ideal for theremin. 

Any help is appreciated. By the way, I did find a few threads on this topic but they are quite old. 

Thank you!

I have Focusrite Scarlett 2i2 interface. I use this to connect my guitar, bass or theremin to my laptop. You can switch the input from instrument (guitar & bass) or line (theremin).

I put my theremin into a wee mixer, along with anything else I want to record and take the output into the USB of my PC.
Quite simple really.
The mixer I use is the Behringer Xenyx Q502USB, currently stands at around £45

I run the D-Lev analog output right into the motherboard line audio input of my PC.  Though this comes from a cheap D/A box. 

An analog heterodyning Theremin might need some extra ultrasonic low pass filtering if the output isn't sufficiently filtered internally within the Theremin and/or PC interface.  You might hear heterodyning artifacts as aliasing.