Thelio hardware problem with Linux Mint

Actually, I've had this problem with both Ubuntu and Linux Mint:

Sound goes away.

I have a speaker amp connected via optical TOSLink to my
System76 Thelio workstation.  The former displays the PCM
rate of the audio connection. Usually, that's 44.1kHz.

Occasionally it will report "no signal", and I have to reboot
the box to get sound back -- and not a soft reboot, but
a big-red-button reboot.

Also, sometimes it has sound dropouts, similar to what used
to happen with USB sound back in the day on earlier systems.
Running "pulseaudio -k" usually clears that up.

I've been through all the potential workarounds on the
System76 knowledgebase for sound problems.

Thing is, the TOSLink connector is usually on the motherboard,
and I don't have problems with them.  But this time, I think
the connector is on a daughterboard, and I suspect it is
connected to the motherboard via USB.

Anyway, it's annoying.  I have a ticket open with System76,
and we'll see if they have something else to suggest.

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-v