What is involved in converting a PC video card to have boot screen on the Mac? I've got a PC video card that I'd like to get boot screen support for on my Mac Pro. In particular, it is a Gigabyte R9 270X. The card is supported on the Mac once it boots, but I would like to get boot screen back since my old 8800GT has been baked in the oven a few too many times by now :-)

I've seen numerous guides on the internet about flashing the BIOS on the video cards and also ones that speak about adding the EFI BIOS, but in the haphazard forum approach, it isn't clear how this all works. To some degree, I've recently come away with the notion that you don't get rid of the existing BIOS, but rather add an EFI partition to it that the Mac would recognize. If that assumption is correct, then it would lead me to believe that adding an EFI BIOS that works on a similar card (R9 280X or 7950 which are both close but not quite) should work since I'm assuming that the existing BIOS would be similar enough to hook in. Failing that, I'm not clear how you would get a card-specific EFI BIOS for boot screen support.

Anyone an expert on this? I'm just really having a hard time trying to sift through all this and hoping to get a more direct answer!
From what I understand, it's not the Mac Pro, it's the graphics card that needs to be flashed so that it's "Apple approved"

For example, on MacUpgrades, they list an Saphire Radeon RX 580
with 8GB RAM


  It has been flashed to work on the Mac Pro 2008 (MacPro 3,1) - Mac Pro
  2012 (MacPro5,1) models.


I ran across a video of the flashing procedure for a newer (but same family) of video cards - though the procedure does require the use of Windows (meaning Bootcamp).

You will need:


GPU-Z to back up your cards firmware
ATIWinFlash to flash the firmware
The EXACT firmware for your Mac and video card


I currently don't have the required components to test/verify this procedure so proceed with caution.  If this is something you are not used to doing, definitely seek out someone who can assist you with this as you run the risk of bricking your GPU.