I have a GTX460 connected to an AV Receiver via HDMI, Audio is setup as 7.1 and gets bitstreamed to the receiver.
In New Vegas I only get music, no voices and no sound effects. Additionally my receiver shows sound to be only stereo and volume settings in game don't work, which means the audio get's directly decoded by the AV Receiver but New Vegas only sends crap.
Why the heck are there no audio settings to setup what kind of speaker setup I have, that alone would at least give me a workaround to this problem.

All the "fixes" mentioned in other threads don't work, it seems like New Vegas just doesn't fully support modern audio setups.

Honestly, Steam install was bad enough (I had the US Version I imported to Europe and had to wait 3 days because my US Version was locked by the EU release date, thanks Bethesda & Steam), and now the game has worse audio support than decade old games which work perfectly fine over HDMI Audio.

I have the same problem on my ATI card with HDMI output, I can only hear music, no other sound effects or character dialogue. But, if I switch and send the sound through anolog into a pair of stereo speakers, I can hear the dialogue and sound effects but no music... Makes no sense to me

I just tested my 5870s and it all works perfectly on my Samsung TV.

Not sure what to suggest as a fix, but wanted to let you know it can and does work, for me at least.

Do you use any codecs packs? That's the only thing that is really popping into my head as a possible cause.