Got it! (Partially. Will finish getting it tomorrow, maybe.)
From
https://ubuntuforums.org/showthread.php?t=1517726:
Found the issue with great support.
Code:
echo autospawn = no >> ~/.pulse/client.conf
killall pulseaudio
LANG=C pulseaudio -vvvv > ~/pulseverbose.log 2>&1
and
Code:
sudo fuser -v /dev/snd/*
made me found conflicting applications at boot
In my case. "timidity" was causing my problem. Within X, I did a "sudo kill timidity", and immediately my Volume control on the pane of KDE's Plasma desktop changed, and the volume control slider produced test clicks. I tried purging timidity, but it seems to want to take half of KDE with it, so I'm gonna hold off until tomorrow to tinker any more with it.
Whew!