I have 2K monitors but Mac is limited to 1920x1080 output??

Hi all,

My MacPro is about 4 years old now. It has the same ATI Radeon HD 5770 it came with. I am running Snow Leopard.

I recently bought 2 DELL U2713H monitors with a 2k capacity, both connected via miniDVI to HDMI.

However in my MacPro system info both resolutions are given as 1920x1080. Is my MacPro too old to output a 2k display? Either because of the graphics card or some other hardware I am unaware of?

Any insights would be greatly appreciated.

Thanks very muchly

S