Hi Jinwa
So for starters, your English is better than mine :-)
Right, so I have done some testing thanks to you guidance. My receiver is a Onkyo HTR380. http://www.intl.onkyo.com/downloads/manuals/pdf/ht-s3305_manual_e.pdf
But I have an atlona 4x4 matrix hdmi switch in the middle so that the same HDMI feed can go to more than one room. I did some recabling as a test, and put the NUC directly into the Onkyo, and with the output going via the HDMI switch to the TV, and volia.....I now have proper 5.1 audio. But, I have no audio in the other rooms, only picture! And if I switch on HDMI audio, I'm getting no audio in the main surround sound room. Argh. What a nightmare! I don't think there is a way to cable this correctly and get what I want. I cant seem to find a setting on that onkyo that allows dual audio output (optical and HDMI).
If I recable back to original config, the media center continues to provide 5.1 output until its rebooted, at which point it reverts to 2 channel. Any creative solution ideas? The only thing I can think of is a HDMI splitter out the back of the NUC, one feed into the Onyko and the other into the HDMI matrix switch.
Of course all of this only solves my 5.1 issue. I still have a lower volume. I've alway found that I needed to turn on Loudness Equalization to have a comparible volume setting between my media centers and other devices (satellite, games consoles etc). Losing this with the NUC is a pain. Im using the same drivers as you (they are common for 7/8)
So I am making some progress, but I guess I need more hardware to achieve the 5.1 goal. And no real hope of achieving the volume fix other than a different machine it seems?