Have a same cpu and chipset just a difference vga for me istead your vga mine one 4670

did you try this option while booting ? When boot loadr appear hit f8 than

-v busratio=21

tried with ideneb 10.5.8 lite and hazard 10.6.2 worked , let me know if its working than you could put premade dsdt to /extra and could use latest efi