My apologies for hijacking the thread, but I've run into the same issue. After upgrading to 10.8.4 via the App Store, my audio no longer works.
In hindsight, I probably should have opted for the Apple Combo Updater rather than opt for the App Store method. I have tried reinstalling the Realtek audio ALC8XY drivers multiple times, rebooting, and repairing disk permissions in various chronological order and cannot restore my sound. I went as far as delving into the S/L/E folder and manually deleting the installed audio kexts (I found these by sorting by "last added"), and then reinstalling the latest audio kexts from MultiBeast, all to no avail.
Is there something I'm doing wrong? Is there a specific kext I should be looking to delete? I'm positive I'm using the latest version of MB for my specified OS (ML). My motherboard is a Gigabyte GA-Z77N-WIFI
Edit: I should mention I attempted to repair permissions using Kext Wizard, but that didn't work either.