interesting. Ok so I've done some research.
There is an amazing amount of misinformation on the web about this. About 75% of the people say Audio via DVI is impossible. One guy had the answer and said that it is certainly possible, but there is no industry standard, and that ATI etc, have developed their own standard, and thus can do it.
From the hundreds of things I've read, people are saying the special ATI DVI-HDMI adapter is necessary in order for it to work, and a straight DVI-->hdmi cable won't work, that the adapter is necessary.
But then, I'm seeing people saying that no adapter is necessary.
on newegg there are specific "DVI to HDMI adapter for 4x series cards" sold by HIS, for 9.99, but also one for 1.99 sold by Rosewill with a reviwer saying it got his audio working. I called Rosewill tech support and didn't get an answer...no wait, just did. He said.. no idea