I compiled Jief_Machak's version of rEFInd, that should have support for initializing graphics cards that have a GOP rom on them. Pretty much any resent graphics card should work. If you don't know what rEFInd is, it's basically a boot manager, Jief said he was not able to boot Windows, but I'm not sure if he had Windows installed via Bootcamp, i.e. CSM, or Bios comparability. Seems if you have Windows installed via EFI/UEFI then this version of rEFInd should be able to boot it, but there maybe some roadblock we'll have to work out. I don't own a MacPro, so I can't test it, so don't be surprised if I screwed something up and it doesn't work, just let me know, and I'll try and figure out what I did wrong. As far as I remember, Apple's EFI looks for the boot.efi in /System/Library/CoreServices/, that is the file that gets blessed by the startup disk utility. I think Apple's Boot Manager, that you get when you hold the Option Key, if you have an EFI video card, also looks in the standard /EFI/Boot location for a file called BootX64.efi, and I think it also looks for other bootable files in the /EFI partition of all GUID disks. Because people using this version of rEFInd don't have EFI boot screens, it becomes necessary to "bless" rEFInd, rather than any other boot manager or boot file, don't worry it won't harm your Mac, and clearing the NVRam will have you right back where you were, without boot screens in you Apple Boot Manager. I'll be uploading the rEFInd files for testers in a few, as soon as my Qemu install of HS wants to start cooperating with me. The normal disclaimers apply, just don't blame me if this software knocks up you teenage daughter, kicks you dog, or burns your house down. --- Post Merged, Nov 17, 2017 --- Here is the link, it includes all the standard rEFInd file, plus refind_GOPX64.efi. That's really the file needed. https://drive.google.com/open?id=1_a3u4DAJKza_xT27lQ5uotW_1DHqG-8t You'll have to disable SIP, or at least disable the part of SIP that blocks access to NVRam, as you'll need to "Bless" the refind_GOPX64.efi. Sorry, 64 bit EFI only, right now. Here is a page that covers how to manually install rEFInd: http://www.rodsbooks.com/refind/installing.html#osx Also in the Doc dir of the zip file, you should find an install.html file. Don't use the install script, it doesn't yet support the refind_GOPX64.efi. Let me know if/how it works.