Hey everyone, sorry to bump an old thread but I'm having a similar problem and can't seem to find a solution. Here's what I've tried so far:
1. Mac Pro 4.1 -> 5.1 with GTX 970 PC (non-flashed). Originally had Yosemite on one HDD, Windows 7 on another HDD.
2. No issues using Startup Disk to restart into Windows 7, and no issues using bootcamp to restart in Yosemite.
3. Upgraded to Sierra.
4. Using startup in Sierra to reboot in Windows 7 works, but bootcamp in Windows 7 is unable to reboot into Sierra, and the computer will only boot in Windows 7.
5. I have gotten around this by using a Windows 7 install disc and holding down C upon startup. Bootcamp was then able to restart in Sierra. I would guess it worked because this method doesn't change Sierra's startup disk option, but I was only able to do it once and don't want to rely on it if possible.
6. I have a GT120 for boot screens, but Windows 7 will only output video through the GT120 when the 970 is also present, and it's not preferable to keep swapping video cards.
6. I tried using a separate install of Yosemite as a sort of startup disk selector, but going from Sierra to Yosemite to Windows 7 results in only being able to reboot in Windows 7 or Yosemite.
7. I did install Clover after reading this thread and following the advice:
https://forums.macrumors.com/thread...c-card-with-boot.2013709/page-3#post-23969568 and was able to successfully boot with it on the GT120 through holding option at startup then choosing Clover, but if I switched over to the 970 the screen would remain black, so I've since reverted to a backup to remove Clover.
8. I tried disabling SIP to see if that would allow bootcamp in Windows 7 to restart in Sierra, but nothing changed; once Sierra is told to boot in another OS, I can't get back to Sierra without boot screens.
9. Holding X upon startup doesn't work either.
10. I've tried resetting the NVRAM before and after installing, then removing Clover, but the above still happens.
11. SMC reset same as above.
So at this point I need some hand holding:
A: Do I need to do a fresh install of Windows 7 with a specific formatting on the disk through bootcamp, etc?
B: Is the Windows 7 version of bootcamp just absolutely unable to play nice with Sierra?
C: Does anyone know the exact steps needed to make Clover show boot screens on a Mac Pro with an Nvidia PC card?
I really feel like I'm missing something with Clover especially when others have claimed success:
http://www.insanelymac.com/forum/to...on-macpro-suing-clover-no-legacy-card-needed/ and I've tried to research it as much as possible, but I'm not sure where I'm going wrong.
Any help or advice would be greatly appreciated.
EDIT:
After trying Clover again with a fresh install of Sierra, and trying every configuration that seemed relevant to my untrained eyes, I couldn't manage to get a boot screen on my 970. I did however, give BootChamp a shot since I already had SIP disabled. While it didn't work right away, re-disabling SIP did make it work. I can now use BootChamp to get to Windows 7, and BootCamp will successfully restart in Sierra.