KVM Switch not using correct resolution

[zark]

I have two identical Samsung 23" monitors plugged into the same nVidia GeFroce GT630 video card.
That works well and I get the correct resolution of 1920x1080.

I want to leave one of the monitors passing through a KVM Switch, however, when I do this, that monitor becomes 'Unknown' and the resolution drops.
I have tried lots of settings using xandra tutorials but they do not work.
I have updated the video drivers to nvidia-current.

Is there anything I can do to make the video display at 1920x1080 even when the monitor passes through the KVM switch?
Thanks