Can't boot anything but Snow Leopard...

Specs: Asus P8Z77-I Deluxe mobo, i5 3570, 16GB Corsair ram, using integrated graphics (Intel 2500 HD).

In the past I've managed to get Yosemite and El Capitan installed on this rig. For some reason I can no longer get it to work. The Unibeast method isn't working for me, it won't start the installer.

If I boot with -x I get immediate errors saying it couldn't allocate pages 0x4705, followed by an error loading kernel cache. If I boot with -v I get further, but I'll either get ACPI errors of some description, or I'll get panic(cpu 0) and it'll blame iopcifamily(2.9) in the log.

I've done a lot of searching and tried all combination of boot flags, changing the OsxAptioFixDrv files, tweaking the bios, making sure I'm using a USB 2.0 port and there are no conflicting components plugged in. I've tried so many things now and I'm getting exhausted, I've been spending days on this and getting nowhere. I've been unable to get the Yosemite or El Capitan installer working at all, and yet I've had no trouble in the past.

The only thing I've been able to work with so far is Snow Leopard. I managed to install it with iBoot using -graphicsenabler=no -v. Downloading the El Capitan updater and trying to update it doesn't help, because I can't boot from Snow Leopard even after using Multibeast (kernel panic on boot unless I use the iBoot disc) so I can't get to the update partition. I've been unable to try and get a copy of Sierra because iBoot forces an incompatible system definition. The Mac I originally used to download El Capitan is too old for the update too.

Please help. :(