The X800XT isn't an option, it requires a Power Mac G5 (AGP). I checked AMD/ATI's site.
Also, when you say dual DVI out, do you mean 2 DVI ports or dual-link DVI? Those are two different things. 2 DVI ports is 2 physical DVI ports, dual-link DVI is one port required for higher resolutions (like the 30" Apple Display has).