I've flailed around trying to get HDMI sound to work on eddy (which is being used for the project's daily Google Hangouts sessions. At first, an HDMI device wasn't available, even with the screen connected and video working fine. I finally solved this by clicking off the "NVIDIA Optimus" BIOS parameter, which apparently selects whether the NVIDIA or Intel video interface is used? However...
Now I can select the HDMI output in all of the settings menus, but sound still comes out of the built-in speakers. I've learned that the audio device should be hw:1,3, but sending sound directly there produces no sound. I've also found in the settings page that setting "HDMI surround 5.1" makes no sound from the internal speakers, whereas "HDMI stereo" does.
In the meantime, we seem to have been able to run a meeting using just the internal speakers.
Another option could be just to get some external powered speakers and plug in to eddy's line out.