The 6.6.x kernel series is LTS and should be fine as a downgrade target (6.7.x not so much so). Unless there’s something specific from the newer kernel versions that you need to drive that system, there shouldn’t be any issues. I’m still on a 6.6-series kernel.
That being said, you could try troubleshooting this from the bottom up rather than the top down.
First, use lspci -v
to verify that the device is being correctly identified and associated with a driver.
Next, invoke alsamixer
and make sure everything is unmuted and your HD audio controller is the first sound device. The last time I had something like this happen to me, the issue turned out to be that the main soundcard slot was being hijacked by an HDMI audio output that I didn’t want and wasn’t using, and that was somehow muting the sound at the audio jack even when I tried to switch to it. A little mucking around in ALSA-level config files fixed everything.
What’s the output of
cat /proc/asound/cards
on your system?