A question to which I hope the answer is "you got it wrong!"
After looking at the "BCM2835 ARM Peripherals" manual page 119 it suggests that the output is only 2 channels (ie says "Frames can contain 1 or 2 audio/data channels in each direction. Each channel can be between 8 and 32 bits wide").
However the HDMI spec states it should "It transmits all ATSC HDTV standards and supports 8-channel, 192kHz, uncompressed digital audio and all currently-available compressed formats (such as Dolby Digital and DTS), HDMI 1.3 adds additional support for new lossless digital audio formats Dolby® TrueHD and DTS-HD Master Audio™" The Raspberry Pi FAQ states its HDMI 1.3a compliant. BUT will the BCM2835 SOC gives us the audio streams with the current drivers?
So.... what *AUDIO* can I get over HDMI (would like DTS-HD Master Audio) do you have a list of what we can get out (like the list of support video resolutions but for audio!)
(yes this is proving educational had not looked at a control register function for a long time!)