I have had the bug report suggestions setup this way for along time as sound is always routed to TV and I don't want it to switch to tinny laptop speakers.
Use sudo -H gedit /etc/pulse/default.pa and find the lines:
Change them to:
I am not an expert, but did you try this?
echo "options snd-hda-intel model=generic" | sudo tee -a /etc/modprobe.d/alsa-base.conf
This has fixed a similar problem on my computer (Ubuntu 18.04).
I know you have mentioned Alsamixer solutions. But just in case. Have you tried to mute the Headphones mic (if any, all) and/or disable loopback on ALSAmixer? There are many threads on XPS 13 and 15 on this matter (and here is a Reddit on it too)
I tried all the reinstall-PulseAudio-alsa suggestions but finally was able to get mine (a fresh install of 19.10) to work by installing the Gnome Extension "Sound Input & Output Device Chooser".
With that extension you get a drop-down list of places for the speakers. When I picked the one into which the speaker was plugged, I got sound.
Note, my ...
Despite using this export:
# paplay needs environment variable exported:
it didn't work.
After months of research found no solution.
In desperation, tried the following and it worked:
Enter the following in contab
# Terminal command: crontab -e
# Detect the name of the display in use