Struggling to remember much about this one.
We had a Jen SX1000 which was a very basic mono synth. It was very broken and could only play one note or something, so we butchered it. Basically we jimmied an audio in directly to the filter section just to see what happened. Somehow it worked and we were able to send audio from our other synths into it and filter the sound. What you hear during the breakdown is our DX21 being filtered by the Jen.