Reinitializing audio and midi -- Nobel-prize discovery made.
Reading the 200th post about "I plugged in my midi keyboard and nothing happened", and expecting an answer of "well, you should have plugged it in BEFORE you started. Quit and reeenter." So I was about to post, "Why can't we have a 'reinitialize audio and midi button somewhere easier than buried in Preferences?" Then I started to wonder about the "MIDI Plug" tool on the play-controls toolbar and wondered if it did that.
Well, I don't have a midi keyboard connected on the Mac, so I bet all my chips on it -- I unplugged the earphones, plugged them back in, played some notes, and, of course, they came out the Mac speakers.
So I twice-pressed the midi button, and hit "play". Lo and behold -- the sound came out the 'earphones' (plugged-in amp, actually).
The new instructions for either "my midi doesn't input" and "it didn't see my earphones change" should be to press that button once or twice as needed. Any reason why not?