Thank you, Tony.
For anyone who wants to use the integrated Intel HD 3000 of Gigabyte Z86-UD3H-B3 MB I put together below a list of steps that worked for me.
Configuration:
MB: GigaByte Z86-UD3H-B3 F10
Intel i5-2500K 3.4GHz
RAM: 8GB
HDD: 1.5TB
Everything works except sleep including restart and shutdown, USB 3.0, video with acceleration, audio, etc. (sleep not tested yet)
Gigabyte Z86-UD3H-B3 - Mountain Lion installation instructions
Used Multibeast 5.0.2
1. Set in BIOS "On-Chip Frame Buffer Size", located in the "Advanced BIOS Features"
2. Install Mountain Lion
3. Copy the entire Extra folder from Mountain Lion Unibeast USB stick to Extra folder on the HDD. If the files are not visible use: "defaults write com.apple.Finder AppleShowAllFiles YES" in the terminal and relaunch Finder
4. Remove AppleHDA and any HDAEnabler*.kext files from System/Library/Extensions
5. Use MultiBeast to select and install:
a. Network driver -> Realtek Gigabit
b. Themes -> Tony theme
c. Drivers & Bootloaders - Chimera 1.11.1
d. Customization -> System Definitions -> Mac Mini - this setting will enable the Apple Intel HD 3000 kexts to kick in and work with dual displays
e. Drivers -> Audio -> Realtek ALC8xx -> Without DSDT -> ALC889
f. Drivers -> Disk -> 3rd Party SATA
g. Drivers -> Miscellaneous -> USB 3.0 - 3rd Party
h. Reboot
IMPORTANT! If the HDD you have installed OS X on requires sectors larger than 512 bytes (e.g. 4096 bytes sectors) you have to follow MacMan's instructions
boot0 Error: The Official Thread to set up Chimera to boot. Otherwise you may end up with the boot0 error
i. Enjoy
NOTE 1: For an unknown reason, the 2nd display boots in 1024x768 resolution despite that the Intel HD 3000 and the monitor are identified correctly. I have changed that monitor's display frequency to 50Hz (PAL) and that did the trick. However, I understand quite a few people have this issue.
NOTE 2: Tony's DSDT for my MB F10 didn't work for me.