Are you talking about the audio driver (separate driver, separate hardware block) or the graphics driver (which controls mixing the audio bitstream with the video stream) ?
In the case of fglrx I believe the graphics part is multichannel-capable but the audio driver is stereo-only.
As far as I know (rumors, rumors) radeon opensource has only minimal HDMI support in 2.0.
When installing fglrx instead, can user access all audio channels via HDMI interface? Three examples:
1 When I play multichannel film which I legally own, that was ripped for purpose of playback (because linux is prevented by hollywood to have those bits; I am not aware of any commercial solution) - yet I have the complete box on the shelf with disc with original - and I have fglrx, can I use HDMI to play all streams? (PS. This way seems to be legal in germany).
2 Im using my machine to make a party and I want to make area sound effects by having multiple boxes getting individual signals
Nothing to do with radeon or fglrx. We're talking about the audio driver here, not the graphics driver.
As Alex said, the register info we recently released should have all the bits required to blend multichannel audio into the HDMI video stream; the issue here is enabling multichannel in the audio driver.