I've got a MacPro with a X1900XT now, but I used OSx86 for a long time before that . So I figured I'd help those interested in using a Titan-like solution for their ATI cards by providing the single-user mode ioregs of my computer.
I have attached two files : the first is the relevant bit of my ioreg, with a monitor attached to the X1900XT, and was taken in single-user mode. The second one was taken with two screens attached, but after startup : the second monitor isn't initialized in SU mode.
Hope it helps someone !