Just in case anyone else has had as much trouble as I did with getting Audio working with Mountain Lion on their Gigabyte GA-EX58-UD5 motherboard, I thought I'd share what worked for me.
1)Used method outlined in http://www.tonymacx8...l-based-pc.html. This got me to a bootable mt lion, but audio didn't work.
2)Downloaded kext wizard 3.7.10 from: http://www.osx86.net/downloads.php?do=file&id=1604
3)Installed dsdt and kexts described by James Littler: http://jameslittler....abyte-ex58-ud5/ using kext wizard. Made sure to rebuild caches and fix permissions!
I'm sure this is a more roundabout way than an expert could devise, but it did get me to a fully working system with working Audio.