OK, as I can't find any info for a definite working fix for your motherboard, your only option is to try EVERY "option" for the STAC9227 codec.
First let's make a backup of your alsa-base.conf:
cp -v /etc/modprobe.d/alsa-base.conf ~/alsa-base.conf
Open alsa-base.conf for editing:
sudo gedit /etc/modprobe.d/alsa-base.conf
You should see a file with a ton of stuff in it .. if it opens a blank file, close without saving .. and try again..
Next you need to add a NEW line at the end of that file .. and enter ONE of the option lines listed below.
then save the file, and reboot to test the sound.
if that ONE option doesn't work .. reopen alsa-base.conf .. and REPLACE the line you added with another one of the options below .. then save, reboot, and test again.
Till you find one that works.
If none of them work .. we'll move on to other options like position_fix and probe_mask.STAC9227 options to try
options snd-hda-intel model=ref
options snd-hda-intel model=ref-no-jd
options snd-hda-intel model=3stack
options snd-hda-intel model=5stack
options snd-hda-intel model=5stack-no-fp
options snd-hda-intel model=dell-3stack
options snd-hda-intel model=dell-bios
options snd-hda-intel model=volknob
options snd-hda-intel model=auto