Here, a screenshot with loaded kext from post 400, so it should work. You have to edit your DSDT, to have the same "hda-gfx" "onboard-x" values for the HDMI and DP device.
My problem was I didn't even get the DP detected (no graphics) but I managed to get it by following a tuto. After that, I tested the sound and it was working. So I didn't have to edit nothing in dsdt. Thanks