Actually that thread you linked to verifies that in that gen of card, Nvidia didn't have an HDMI audio option. ATI did, but not Nvidia. Nvidia didn't come out with a true HDMI audio option until the 400 series.
Don't expect anything but 400 series cards and beyond to pass through both video and audio. The 200 series had a funky mini cable that was supposed to pass onboard audio to the HDMI port on the GPU via connecting it to the MB header and a small port on the GPU, but those never worked.
Even the current gen with HDMI A/V passthrough can be hit and miss depending what peripherals you're using. I just tried a 660 Ti that refused to show the Nvidia HD Audio device as ready for use. It always showed it as unplugged. I've seen others with similar stories.
I don't even feel Nvidia has better driver support lately, and am seriously considering going AMD.