Heya Paul
If you're talking about what I think you're talking about, it unfortunately isn't possible to do it quite that way; the major/minor information encoded in the device files will be interpereted locally at the NFS client.
For example, if your Rio /dev/audio happens to have the same major/minor as your sound card on the machine you're seeing the filesystem from, you'll open the sound card on that machine, not the Rio.
The only way to do it AFAIK would be to build some kind of proxy, but it would probably be a pretty evil project.
Now if you want to write a Windows sound driver that backends to a shoutcast stream instead of a sound card, I'd be really interested in that...
--ZS