The OP was asking about *audio*. DVI does not support audio. Mini DisplayPort potentially does, but it is not clear MDP to HDMI adaptors supporting audio exist or are readily identifiable vs. those that do.
MDP to HDMI adapters that support audio DO exist already, and most of them that support it are indeed readily identifiable in major sites (eg. apple store, monoprice, amazon, etc).
According to the Apple 2010 MP specs, audio over MDP (hence HDMI) is supported. Such implementation is already working flawlessly in the latest MBP an iMacs, so I don't see a reason why this wouldn't work in the new MPs...
The real interesting question is if audio over MDP-HDMI
will work in 2009 MPs using the officially supported 5870, and/or the so-far officially unsupported 5770,
and if it will work under previous MPs running both officially unsupported options, since it's not clear whether audio over MDP-HDMI is entirely hardware-driven, software/firmware driven, or both.
I surely hope the 5770 works in 2009 Quads, audio included, so I can get rid of both my 4870 and GT120... the 4870 is a power hog, and the sole reason I got the GT120 is to drive a 3rd display. All of this would be solved with the 5770... so come on Apple!!! the only reason I can think of for not supporting the 5770 on 2009 MPs is greed, trying to maintain sales for all cards. Hope this is not the case for long.