echo sad0_rates 0x1ee0 > /proc/asound/card0/eld#3.0
echo speakers 0x4f > /proc/asound/card0/eld#3.0
echo sad0_channels 8 > /proc/asound/card0/eld#3.0
echo sad0_bits 0xe0000 > /proc/asound/card0/eld#3.0
These were the lines I needed for Multichannel LPCM on Intel Sandy Bridge (until we got proper kernel support).
Of course this is a workaround. If the ATI driver does not support the LPCM output, than I think this is not working.
But If the problem is just that the driver does not parse EDID/ELD data properly, this could be a help.
ANy other valuse in ELD can be overwritten as well. Of course you have to adjust the values to your own system.
It is a trial and error process.
And you can test if LPCM is working with running X server type:
speaker-test -Dhdmi -c6
For a 192k bitrate:
speaker-test -Dhdmi -c6 -r192000
Instead of "hdmi" you can write any value that suits your config (eg. "plughw:0,8")
Edit: You have to be in super user mode for that so first do: