it is possible that you need to change one line in your default.pa - add the correct sink you found out which is working using "speaker-test -D hw:0,x -c2" - be sure all 4 possible spdif channels are unmuted (OO) with alsamixer. use nv binary driver. the x is the device number you get with "aplay -l". for onboard the card number is always 0, but of course not for a desktop system with dedicated gfx card.
radeon.audio=1 is for the open-source driver, the proprietary driver doesn't use it. With nvidia you still need the proprietary driver for HDMI audio - Nouveau support for it won't come before the 3.2 or 3.3 kernel.
Intel is a different matter. The HDMI audio is a codec chip connected to the onboard sound controller (or even integrated into it?), and the only thing that relates it to the graphics is that it happens to use the same HDMI connection for its output.
My first time on this forum.
I am having a similar problem - although I have an Intel i5 processor and HD 5700 series card. Everything was working fine in Kubuntu 11.04 but after upgrade to 11.10 no sound at all. Adding radeon.audio=1 to grub has made no difference.
Any suggestions as to where else I should look?