Hi there!
Thanks to this great forum and excellent contributors (Cindori, Netkas, The Rominator, Pipolo to name just a few) I have been able to successfully:
- create an EFI ROM for and flash a SAPPHIRE VAPOR-X HD 4870 2GB GDDR5 PCI-E
http://www.sapphiretech.com/presentation/product/?psn=000101&pid=217
- have Mac OSX 10.6.2 boot with a SAPPHIRE HD 4870 X2 2G GDDR5 PCI-E
http://www.sapphiretech.com/presentation/product/?psn=0001&pid=180 (ID = 0x94411002) with the help of the Natit injector (for Sapphire 4870 cards) of Cindori's ATI Flashing Tool
However, there are still some problems / open issues for which I will need some help:
I can't seem to create EFI ROM('s) for the SAPPHIRE HD 4870 X2. When I follow pipomolo42's procedure on https://forums.macrumors.com/showthread.php?p=7297669 I always get an error message. The procedure worked just fine for the ROM of my SAPPHIRE VAPOR-X HD 4870 2GB so I'm guessing the problem is related to the ROM('s) itself. Is there a way to create EFI ROM('s) for the SAPPHIRE HD 4870 X2 2G GDDR5 PCI-E? If yes, what is the procedure? Do I need to convert both ROM's or just one? If yes, which one? I've added the original ROM's to this post in case one of the pro's around here want to give it a try 
Since I can't create EFI ROM's for the SAPPHIRE HD 4870 X2 I have installed Netkas's Natit.kext using Cindori's wonderful ATI Flashing Tool (thanks guys!). However, with the Natit.kext installed I'm having problems opening .jpg files (pictures) in both the Preview and iPhoto applications: When opening a .jpg file with Preview the app launches and opens the file but shows a blank window/image. In iPhoto, when I double click on a picture preview to open the picture in full view I also get no picture (but instead the list with previews remains visible), when I select a picture preview and go to "edit in full screen" iPhoto switches to full screen mode, shows the tool bars but does not show the picture (but a black screen instead), when I go into Faces mode to identify faces, the screens shows the square face boxes as if the actual picture is there but it's not (again, the list with picture previews remains visible with the square face boxes on top). As this is a major issue I can't really use the SAPPHIRE HD 4870 X2 under Mac OSX for the time being.
When running the QE_CI tester in the ATI Flashing Tool it seems QE is NOT enabled. This for both the flashed SAPPHIRE VAPOR-X HD 4870 2GB and the SAPPHIRE HD 4870 X2 enabled with the Natit.kext. Is this normal?
Any suggestion or help for the above will be highly appreciated!
Greetz,
Bruno