Not sure what I can add to the discussion but here are my experiences on running Lion (10.7 below) with XFX HD-577X-ZMF3 and Apple Cinema Display on MiniDP. My system info is in signature.
OSX 10.6.7: Graphics work OOB. Used GraphicsEnabler=Yes.
OSX 10.6.8: Graphics work with modifications. Used GraphicsEnabler=Yes. Also, used ATISupport, ATIFramebuffer, and ATI5000Controller from 10.6.7 to get fully working graphics.
OSX 10.7: Black screen. I have found two solution, none of which are perfect:
I can get the ACD working in 10.7 if I replace the ATI kexts with the ATI kexts from 10.6.7 or from 10.6.8 (with modifications listed above). Problem with both these methods is that the system is really slow; for example, Launchpad take 5+ sec to load and iWork does not show cursor. My guess is no acceleration.
The second solution involves the vanilla 10.7 kexts, but with minor edit to the ATI5000Controller kext. In info.plist I rename the Langur framebuffer to Velvet. This gets 10.7 and ADP to load on MiniDP. Still, however, the system is really slow--no acceleration.
For what it is worth the problem seems to be that Chimera injects the Velvet framebuffer for my card. If you check ATI5000Controller on 10.7, however, only four framebuffers are listed and Velvet is not one of them. The first solution above use old kexts that include the Velvet framebuffer and the second solution simply tricks the system to load the Langur framebuffer.
From reading other posts here at tonymacx86 and the netkas forum, it seems that there may be a third solution. This solution assumes that the 10.7 kexts already work with fine my card, but that the MiniDP is not loaded with the vanilla framebuffer since my card is not a reference card. This can easily be verified by using another screen that has a DVI connector on my card (will try this weekend). If this is the case, then it should be possible to activate the MiniDP port on the card and run vanilla in 10.7.
Any comments and suggestions appreciated.