Michael Junck has produced a German language radio show about the Optigan. It features lots of music he made (covers, mash-ups, etc) using time-stretched Optigan® samples. Here’s a version of the Spice Girls “Wannabe” that he made. Maybe I should brush up on my German- I took four years of it in highschool but can hardly remember a damn thing!
Michael has also made some simple transcriptions of various Optigan® riffs which he says may or may not be of use to anyone else. I haven’t had a close look at his shorthand, but I’ll paste his list here in case anyone might find it useful: