Happily, I got the Uno back as a Midi Input setting option as soon as I switch midi drivers from CoreMidi to Apple Synth and then back. I'm wondering if I should be setting all ports to the Uno, and if the Midi-In light on the Uno ever does anything but flicker.
Perhaps I'm mistaken in expecting to hear the BBox rhythm section over my keyboard phones under any circumstances?—although I don't see otherwise what the point of a midi out to the keyboard would really be.
Live Help says their main tech guy is out for the week, so we'll see Monday if there's anything left of my problems and/or computer.