First things to do:
1. Go to matrox's site and get the latest firmware and powerdesk.
2. Add 4320x900 and 5040x1050 in powerdesk.
3. Follow my
guide to add 4320x900 and 5040x1050 as custom resolutions.
--It should be easy enough to use the tool, but some people have issues with the tool, so you may need to add them manually in which the guide explains it.
4. Try and change your resolution in windows to either.
EDIT: I don't have a TH2Go to test if this works, but I imagine it does.
Though I'm wondering, if you have an eyefinity enabled card (everything 5000 series and up) then why don't you just use eyefinity.
All you would need is an active miniDP->DVI adapter of a miniDP->VGA adapter and you'd be golden.