Switch Rez is a pain to use and it is very finicky. I removed it from all my Catalyst machines because of the problems it was causing.

Use a DVI detective on the center of the TH2G so that it thinks the EDID is the same as the sides.

Something important to know is that the sides might be in VGA mode which is why the center is not working. If your output devices on the sides are generating an EDID which tells the TH2G that they are analog then the TH2G will send analog as a priority and disregard the center.

You can verify this by making sure you are using DVI-D cable and not DVI-I cables with the extra quad pins next to the ground slit.