I have the same board (with UEFI bios 1b) and Sapphire HD6870 and I have clover for my system (yosemite). For me, the easiest path to setup are:
1. setup Yosemite using Unibeast/Multibeast
2. Make sure everything works (except imessage)
3. Download Clover boot loader and Clover Configurator (optional but much easier to configure your system including iMessage)
4. Install Clover (I used TonyMac's
http://www.tonymacx86.com/yosemite-desktop-guides/144426-how-install-os-x-yosemite-using-clover.html starting from step4)
5. Do not reboot. Use Clover configurator to configure your system. For me, I just need to check "Inject ATI" and provided frame buffer personality, port, etc ...
6. Reboot the system.
7. Go into BIOS and make sure you choose UEFI device instead of standard BIOD device as primary boot
8. Save a and restart.
If everything works, you should be able to login Yosemite. From there, you need to configure iMessage to work. I used the guide "How to fix iMessage" by JayMonkey. You also need iMessage debug program to obtain system values and you can should use Clover configurator to input the system values. I was using Lexon's instruction (
http://www.tonymacx86.com/yosemite-...ll-os-x-yosemite-using-clover.html#post893000) as guideline. Keep on trying until you get the message calling Apple with customer code. Then you just need to call Apple to unblock. There were some issues for me with mouse shutter, display too bright, and not all video ports are working ( I used two displays). Changing appropriate fram buffer personality fixed all those issues.
Good luck and let me know if you have any questions. I'm not an expert with Hackintosh but will try to answer based on what I know ;-)
Cheers,
ttb