What'd be MUCH better would be some way to have a client on the Rio itself that responds to commands, with good feedback, even if it's just "PLAY 3a95" or something. I don't suppose anyone's found any hooks in the player executable that'll let you shove a command at it? especially hooks with feedback?

Um, you just described Displayserver.

Of course, Displayserver was much nicer than that. It gave an actual live screen shot of the player display, and let you remotely control its user interface, from a web browser. (Note: Description is the Empeg Car version of the product, I do not know how far Frank got in the Receiver implementation of it.)