I'm using an Ultra 1 to play audio, with audioplay.

It works, but the problem is, it plays it both to the back-panel jack
and to the internal speaker(s?).  I want to shut off the latter, so the
machine itself is quiet and the sound comes entirely from the external
sound system.

I've played with mixerctl and audioctl, and everything that shuts off
sound from the machine also shuts off sound to the external jacks.
(I've tried all four of the back-panel jacks; only two of them produce
sound - the ones marked with the headphone icon and the
arrow-leaving-circle icon.  Interestingly, plugging into the headphone
jack makes the sound from the internal speakers significantly louder.)

Will I have to open it up and unplug the speaker (or cut a wire, or
some such) to silence the built-in sound?

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