Damn. You guys are good. I dunno why I even thought it could be a challenge.
It is a Gigabyte 3D1, Dual 6600GT SLI on a Single Card.
Originally sold for $500 in a bundle with a Gigabyte GA-K8NXP-SLI, it was on par or better than the X850 Ultra / 6800 Ultra. According to some sites, only 1000 of them were made, but even if it's not true, it's still a damn rare vídeo card.
Even tho most websites just say that it only works with the GA-K8NXP-SLI, it will also work with some other models like the GA-8N-SLI and it's three variants, The GA-K8N-SLI and it's variants and basically every Gigabyte Card that has one of these:
The way Gigabyte was able to do this, is by splitting the top x16 pci-ex slot into 2 x8. That card when plugged in normal mode will make the top slot work as a x16, when in sli mode will make the top x8 and the 2nd one as x8 too.
I've read that in other motherboards it does work as a normal 6600GT, unless some new drivers unlocked the ability to use it on normal motherboards. I'll test it this afternoon.
I did get the original Motherboard CD, the S-Video output conector, and extra bracket for support.
