The 3870 makes sense since it does seem to live happily next to its EFI compatible HD 2600XT when booted into OS X. You're almost there already.![]()
What do you mean by "live happily" ? did you get a display (grey screen, volume selector, rEFIt maybe ?) in EFI on this card ? This would mean that the 2600 firmware already handles the 3870, and only the Mac OS X driver needs to be updated ... Or did it simply "not crash" ?