Updated 10/16/2016 to reflect a small installation change to regain HDMI audio functionality in Sierra . This solution will work in Sierra as well as several previous versions of MacOS. Keep in mind that I didn't create the tools I only figured out how to use them. Credit for the kext goes to andrejkw at macrumors. Your mileage may vary but this is the easiest solution I've found. It has worked for many others. Definitely worth a try.
1. Download package located here
https://www.dropbox.com/s/8hay1m0rec93vvo/HDMIAudio-1.0.dmg?dl=0
2. Mount HDMIAudio-1.0 disk image
3. Mount your EFI partition. You may need to use
Clover Configurator or similar tool to do this.
3. Copy HDMIAudio.kext from the HDMIAudio disk image to EFI/Clover/Kexts/
Other
4. Reboot. (x2) Clover may hang on the initial boot attempt, if so a restart of the computer should have you up and running.
There you have it, a simple file copy.
After the reboot I had working HDMI Audio.
Hopefully this helps someone else.
If you're confused there is a quick rundown in this video.
*the video was for a previous version of MacOS. Make note of the kext folder in this updated guide!
*Don't forget to select the proper output! System Preferences/Sound/output or hold the Option key while clicking volume icon.
So now you have HDMI audio, but what about volume control? OSX doesn't support volume control of HDMI devices natively. Use one of the utilities below to enable it.
Audio Hijack
Sound Siphon