The 12.3's work afaik with no problems, I don't use HDMI for audio, but I have read about the issue and it's pretty poor it's not been properly fixed yet as they had working ones in the 12.3's.
Get 12.3 drivers, run it to unpack the files, either just uninstal the HDMI drivers from the AMD installer and just run the 12.3's HDMI package, or:
***W7 only***
Cut the 12.3 HDMI drivers from the package and swap them with the 13.1 HDMI package after unpacking to your C drive, uninstall AMD drivers/caps-restart.
Use AMD's new AMD Uninstall Utiity as long as your not using W8-restart.
Goto where you unpacked the AMD driver and run setup>hopefully, working HDMI.
On failing that, if it's for an amp, I also read that a splitter running between the amp and screen, forces the audio to kick in as it should.