^^ Congrats ennogs!
Now that you've learned a thing or two I'd keep plugging at options, perhaps search and ask on Asus support forums. I'm kind of troubled that there is no apparent passthrough of audio, that you don't have that DD/DTS setting. Dolby Digital Live is going to transcode all sources to DD. Not that this is necessarily a bad thing, but it's not the true audio source and it's going to take processing power to transcode.
If feeling particularly adventurous you can try these custom drivers:
I haven't done so, but there are multiple topics indicating that they are superior to Asus. Just a thought - I'd personally continue to study and determine the source of your passthrough issue.