Unlike most camcorders, the 5D Mk III with its new Firmware update doesn't export the sound digitally through the HDMI. Here we show you how to get around this and what you need to watch out for.
EDIT - I do need to point out something I didn't mention. You will find that the video and audio are about 5 frames out. EDIT (7/5) - Just heard from Atomos that they are working on a firmware update for the Ninja 2 that will solve this - hopefully should be released within the week.