Well, the bad news is I could not get enough time last night to install the 4850 into my HTPC - it's in an 19" A/V rack and the Silverstone case I use doesn't have holes to attach slides, so it's quite a hassle to pull the unit out to make hardware changes. My wife really doesn't like me working on computer stuff in the evening - ah when I was single - I used to stay up all night working on a new build...
The good news is that I did manage to install it into my desktop system running Vista. So at least I could get the drivers installed and such.
It appears to be installing a version of Cat 8.5. The audio driver controls are not integrated into CCC - there are no audio options (HDMI or otherwise) in CCC.
An HDMI sound device does show up in the Vista sound control panel, but it is odd, it just sees stereo speakers. Now, maybe it won't let me do anything else since I don't have it plugged into an HDMI monitor, but it does seem odd that there aren't any more capabilities visible.
I'm can VPN into my house and play with it remotely, so I'm going to poke around some more and see if I can figure why more adjustments aren't available...