R9 280X not working in 5.1 10.9.4

Hi

After some reading, I just went out and bought a 280X 3GB to put in my 2010 5.1 Mac Pro.

I previously had an ATI 5870 1GB.

I didn't flash the card, so I didn't expect a boot screen. I waited patiently as everything spun up. Boot chime on the internal speaker as per usual.

Gfx card spins up and everything seems normal. Initial boot was with two displays: DVI and MDp. Then I fell back to just MDp (Apple 24" cinema LED). And then just the Dell 24" via DVI.

Regardless of combo, I get two black screens. I was under the impression this would work out of the box, since I'm pretty current? Kind of disappointed.

Card is a XFX DD Black edition and it seems nice and isn't too power hungry. It was spinning nice and quiet.

It says on board UEFI BIOS. Can it be that it defaults to an incompatible BIOS? Because this SHOULD work, right?

Thanks a bunch for chiming in... I value your experience.

You are indeed right. I first tried the provided adaptor where two 6-pin female heads lead to one 8-pin male. I put one of my 6-pin heads into this and turned it into an "8-pin". The other 6-pin was left dangling.

Then I tried omitting the adaptor, and plugged my 6-pin into the 8-pin leaving two small holes "left over". I had read about someone else who did this with success on another card. Was worth a shot.

At no point did I use any extra power source apart from what I already have. Nor will I.

I will by any adaptor that will fix my problem, but I researched the card to fall within the 225W (in practical use) limit.

Even the packaging on the card calls the 8-pin (or the 150W line) "recommended".

You get lots of karma points if you can solve this with an adaptor solution... Thanks for taking the time. I appreciate it a lot.

My adapter has two fully loaded 6-pin females (each has 6 wires) into one 8-pin male.

Messing with the ROM would be doable, but it's what I hoped to avoid. I was really under the impression that this would be a smooth affair. But since most talk is of NVIDIA cards, what you're telling me is good information.

I'd probably rather return the card, but with this behind me I'm not that fired up to try with another brand...

I know you sell cards, so that makes your input even more valuable.

Do you think I have a power issue, or is it something else? What was your bad experience with XFX?

OK.

Thanks a lot for the heads up. I'll try the adaptor thing, but won't mess with ROM this time around.

It's definitely good to know that that the Radeons might not "simply work". Mostly, I wanted the extra RAM for Resolve and wanted to stay with ATI and OpenCL since I'm mostly in FCPX anyway.

I take it with a GTX 780 I could probably just pop it in there? That sticky seems pretty conclusive? But 4k needs to be @60Hz though... oh, well...