I was able to achieve success installing Yosemite 10.10 on my build, so I wrote this guide to help others do it too. Note: I wrote this after a few rebuilds so I may have forgotten some bits. But use your head and take it one step at a time. Google = win.

PC Specs:

✓ BIOS: F11

✓ CPU: Intel Core i5 @ 3.29 GHz

✓ GPU: Nvidia GeForce GTS 250 1024 MB

✓ RAM: Kingston HyperX 16 GB (4x4GB) DDR3 1333 MHz

✓ Keyboard: Apple Keyboard, USB

✓ Mouse: USB- Xornet 5 Button

Working:

Everything except Sleep. (may be resolved using a kext but I’m not concerned with it. Please update this post if you find a solution)

Install Steps:

▪ Download Yosemite from App Store on a Mac.

▪ Download this pack I made of the kexts and tools needed: https://mega.co.nz/#!kNIHkZiD!VzTz9aNT-gS-buDiYgyAJZXlJ2ig2Nw9vi4x7LlbtnM

▪ Make USB installer with Unibaest on that Mac to a USB at size 16gb or more.

▪ Reboot, hit Delete at BIOS, select Northbridge, Onboard graphics (just for now)

▪ Reboot, plug monitor into onboard plug on motherboard (at top)

▪ Hit F11 to make BIOS boot from specific drive, select the USB, install Yosemite to a HDD (you may need to format the drive with Disk Utility first, make sure GUID not MBR)

▪ Reboot into your previous OSX (if you have one), if not then plug the HDD you just installed Yosemite to into another OS X machine.

▪ Open Multibaest 10.10 from Tools folder, select EasyBaest then Build (make sure you select correct partition).

▪ You MUST select “GraphicsEnabler=Yes” option under Boot Options.

▪ Once done, you MUST put the DSDT.aml file in the new /Extra/ folder. Without this it didn’t boot at all for me (kernel panic’d)

▪ /Extras/ should now have DSDT.aml, modules, org.chameleon.boot.plist. Don’t do anything for now, keep it simple to narrow any issues. This should be all the essentials you need for first boot.

Try booting it on your main rig now, it should boot. Remember to tell your BIOS to switch back to PCI Express graphics (if you’re using one).

If it doesn’t boot, follow next step. If it does boot, skip to [It Booted] below.

If it didn’t boot yet, you may need to put the included mach_kernel in the system folder. Also you might need to use Kext Utility.app to repair kext permissions as it may not have been done already. That should make it boot. If still not booting, boot using -v to read the error message(s) you see and search online, it may be related to other hardware you have that differs from mine.

[It Booted] Great, now make a backup immediately using CCC or SuperDuper. Do not use Disk Utility, it will screw with file permissions.

Once backed up, next go ahead and install the tweaks below. Put each one in /System/Extensions/ except the Ethernet with goes inside another kext.

Kexts: (Remember these are specifically for GA-P55m-UD2 mobo. May not work on other hardware.)

Make sure you downloaded the pack I linked above, here's the link again: https://mega.co.nz/#!kNIHkZiD!VzTz9aNT-gS-buDiYgyAJZXlJ2ig2Nw9vi4x7LlbtnM

Audio- AppleHDA.kext

Ethernet- AppleBCM5701Ethernet.kext

USB2- IOUSBFamily.kext, IOUSBMassStorageClass.kext, JMicronATA.kext

USB3- AppleUSBXHCI.kext (unconfirmed)

Once you’ve installed these where they belong, BE SURE to use Kext Utility.app to repair permissions before rebooting.

You should reboot and notice your audio, ethernet, and usb are working fine. If not, try deleting them, and putting the kext files on the desktop and use KextBeast.app to install. Also try using Disk Utility.app to repair whole disk permissions.

If things worked fine, these are the last steps. Move the SMBIOS.plist file to the /Extra/ folder, this lets you connect to the App Store and iCloud successfully. Also you may want to open Multibeast again and go to Customize, SSDT, and pick and install which CPU you have.

If you followed this guide you should have a smooth running Yosemite OSX 10.10 installation running now. Make one more backup using CCC or SuperDuper and away you go!