Alas, when I plugged in the headphones and the Thunderbolt connector at the same time, I jiggled loose the fan connection within the laptop (I didn't know this at the time), and very rapidly, the computer's fan ran constantly (and loudly) and the computer totally forgot about its internal speakers, never mind the headphones. Thus, the trips to the Apple store on Monday (to drop it off) and Tuesday (to pick it back up). During the week, I got my new Sennheiser headphones (reviewed earlier, and Still Amazingly Wonderful), and today, I got to attempt, once again, the Movie with Headphones on a Nice Monitor experiment.
It is every bit as good as I had thought it would be.
But after 10ish minutes of Star Trek Into Darkness, I'm going to go back downstairs and watch TRMS on the Tivo, then go to bed.
The sound display was a little weird. It still didn't show the headphones, so I set it to "internal speakers" and crossed my fingers. It then displayed "Headphones" instead of internal speakers. I don't really care; it worked.