- Instructions -
1. Download and install Soundflower
2. Launch Soundflowerbed.
3. Set (2ch) to HDMI (or the name of your output device)
4. Open System Preferences / Sound
4b. Set "Play sound effects through" to "Soundflower (2ch)"
5. Select the "Output" tab
5b. Select "Soundflower (2ch)"
Now, Soundflower should be acting as a software mixer that enables the volume controls in OS X to work with HDMI audio. The volume controls in the menu bar should no longer be disabled and, if your keyboard supports it, you should be able to control the volume/mute right from your keyboard.