I'm now using 0x16260006 which enables HDMI video.
Here's my new file
HD5500.zip works well, but no HDMI audio
HDMI_Audio.zip has HDMI audio but loses mouse after sleep. I still haven't figure out the fix for that yet.
Only difference between the 2 DSDTs are renaming B0D3 to HDAU to allow HDMI audio and renaming GFX0 to IGPU. Those 2 changes causes KP with the HD5500 config file.
With the config and DSDT changes in HDMI_Audio, sleep is not working properly and loses mouse.
I'm using ApplePS2Controller for mouse and not voodoops2controller, it works but no trackstick scrolling.
Hope you or anyone with this model to give my files a try and help make it better. I have limited time to test these days.
HD5500.zip
HDMI_Audio.zip
ApplePS2Controller.kext.zip