Limited Resolution on Intel Core i Series Motherboards
Solution 1:
It is the limitation of the motherboard. Even the older generations does support 2560x1600. the limitation is built by the motherboard manufacturers.
Ref: http://www.bit-tech.net/hardware/graphics/2010/01/25/intel-gma-hd-graphics-performance/1
Consider google "H55 DVI-D" if you want to search for boards supporting it.