I am in similar situation, my HP ZR30W has 2560x1600 res and both DVI and DisplayPort are working fine on ati and nvidia I can set 2560x1600 no problems I tried both DVI and DP are working fine.
Obviously on my lousy intel HD 4600 (HD my a...;P) I can only set 1280x800. Motherboard I have, gryphon z87 has DVI (max 1920x1200) and HDMI (max 4k). So DVI to monitors DVI of course don't work, why should it is only DVI so it should only give me 1280x800 according to asus or intel who knows whose fault it is.
Well I thought, let's get HDMI to DVI cable as it says 4k@24hz and 2560x1600@60hz so I bought one and what did it give me, NOTHING stil 1280x800!!!
Now I could be stupid and try getting HDMI to DisplayPort cable as a last try but something is telling me that this solution is also not going to work.
So THANK YOU intel for nothing your HD graphic card SUCKS big time and is totally useless even nvidia nvs295 (old piece of junk) is giving me 2560x1600.
I will have to spend more cash on gtx 670 probably, I didn't wanted to because I planned to wait until next gen but nothing else left to do....
And also asus support sucks they have no idea what they are talking about.