I see that the two chips are pin for pin compatable and it appears that you could replace the problematic VIA 2021 w the newer more mac friendly - realtec chip ALC885.
Now this brings up some questions as to the chips relationship with the bios UEFI - and support for the ALC885 when replacing the VIA w the Realtec - this is somewhat of an unknown - but as they are both conforming to the intel HD audio standard. http://www.intel.com/content/www/us/en/standards/high-definition-audio-specification.html
and that when it was done the OSX did work w speaker and mic with the new ALC885 chip - from the two ports on the rear of the MB ( not sure about HDMI though)
But sound in OSX and Linux do work -