Zotac GTX 570 + Mac Pro 2.26 = Black Screen

I've searched all over but I can't seem to find a solution, so I thought I'd try a direct post.

I just got a Zotac GTX 570 to put in my Mac Pro, followed the main installation guide (installed Lion DP 10.7.2, edited the NVDAGF100Hal.kext (trying both 1081 and 1086 as device ID), enabled graphics enabler directly in the com.apple.boot.plist, shut down and installed the card, restarted...

But I get nothing. Nada. I get a black screen.

Also, I tried the ATY_Init file, but I may have gotten a little out of my depth there.

I'm not sure where I'm going wrong. I feel like I should at least get something, some sort of display reaction, but I'm getting nothing. Any help or advice would be greatly appreciated. Thanks

EDIT: When booting with a helper card (myHD4870), I can see the GTX in the system.

It's identified as Nvidia Geforce GTX 570 SLI, but the vram amount is wrong, and when I click on PCI information, it gives an error message.

Also

Also, another weird thing is that when I leave only the GTX in the machine and boot, I can't see anything on the monitor. But when I remotely log in from another computer, it seems to be working.

I'm going to buy a Zotac graphic card like yours and I gotta say this error scares me as hell. An answer for this will be great for me too.

EDIT:

But looks like you assembled your graphics card on a Mac Pro. Didn't notice about that.

The Zotac GTX 460 1gb I got this week had the same issue, I found it works properly only with a single monitor connected to the hdmi port. Plugging in another monitor or a secondary gfx card causes issues. I'm still researching a solution to this, if I get it all working I'll let you know