Hi all,
Wow but this is a long thread. My experience so far with a Mac Pro 1,1 and a ASUS GTX750Ti-PH-2GD5, running Yosemite 10.10.5:
I simply could not get this card to work in my Mac. I started by installing the latest web drivers which automatically added 'nvda_drv=1' to my boot-args. Depending on which slot I installed it in, the card would either not be recognised at all or would be recognised correctly as a 750Ti 2GB, but no display output would be shown / no screens detected on any ports. I later found out that this was down to the PCIe speed for the slot it was installed in. So it would be recognised in 1x or 4x mode, but not in 8x or 16x. I found this out by changing the speeds for each slot using the Expansion Slot Tool that comes with OSX.
I did a bit more research and found that nobody else had had much luck with this particular ASUS card and indeed some other manufacturers' cards. I tried flashing other video BIOSes with mixed results but nothing that worked in a stable manner. I then tried the Gigabyte BIOS. I didn't realise, but the card that this BIOS came from has the 6-pin power cable, which of course the ASUS card does not. The VBIOS prevented the computer from booting and displayed a message that said to plug in the PCIe power cable (This was shown when installed in my PC, of course the Mac would just show a blank screen), which of course wasn't possible, rendering the card effectively bricked. The only way I got around this was to lift the CS pin of the flash IC on the back of the card to let the PC boot (using the internal gfx chip) and then connect it back after booting windows to run nvflash and restore the original VBIOS. Hair-raising! But I digress...
Anyway, I then took the one ASUS BIOS that some people had had some luck with, ie the ASUS 750Ti Strix BIOS. This worked OK, but would cause my PC to crash after a few minutes. I figured it was because of the much higher clock rate that the Strix card uses, so I used the Kepler Bios Tweaker app to change the clocks to match the original BIOS's clock rates and reflashed. This was stable in Windows!! So I plugged it into my Mac as a second card next to my (working) Radeon 5450 with high hopes...
..and the Mac booted up! Using two displays, one connected to the Radeon and one to the GTX750Ti, in a slot set at 4X speed. However, it would crash at the login screen. Balls. Again, it would only be recognised (now detected as a 'Nvidia Chip' or something like that, ie not correctly identified as a GTX750Ti 2GB anymore) if in a slot at 1x or 4x, the Mac would completely ignore it at 8x or 16x.
So, I'm now wondering if there is a power issue here. I know that the 1,1 Mac Pro has PCIe 1.1 and cannot support as much power through the PCIe slot itself as PCIe 2.0 (as in my PC, where the card works flawlessly). Of course, the GTX750Ti is bus-powered and I have a feeling that it is not getting enough juice from the PCIe slot on my Mac Pro motherboard. I feel the slot speed and the power issue are related, but of course I could be wrong.
I've now given up trying to get it to work in my Mac. I am going to sell it and buy another card, I was thinking about an EVGA 750Ti FTW card, as this has an external power connector so should (in theory) draw less power from the m/b. The other option is the Gigabyte OC 750Ti, which also has the external power connector but does not have DisplayPort, which I would like to use to drive a 4K monitor in future. Both of these cards are confirmed working under Yosemite in Hackintoshes, but I can find very little information about whether they will work in a 1,1 Mac Pro. I am operating on a hunch at this stage.
I would welcome any comments on my findings, as well as any recommendations about which card to try next. Thanks for listening...
