Thanks for the responses, dave_dore and Torsten. I'm finding a few things to be true more and more often: 1) nothing happens by magic (there's always a reason), and 2) buying ready-made, multi-purpose stuff usually adds latency and complications. I'm guessing that the Windows 10 USB port could be served by one side of an optocoupler -- the other side of which could take the signal from the Din out to light up its LED. Any opinions?
So everyone currently accessing Cantabile through a keyboard is buying one of these ready-made cables or converters, huh?. Interesting.