HD audio may or may not be passed through. There are long discussions about this so let's not duplicate past discussions about HD audio passthrough.
In short you need to play the content on a player that can't render the audio (no speakers) and connect it up so the first renderer is your receiver.
I have Samsung 46" UE46ES7005U LED Smart TV and recently I am unable to hear sound on my Pioneer 921 receiver when playing from universal serial bus key. To hear sound I have to increase the volume on my TV. It is a mp4 video file.