Probably the quickest solution is to replace your graphics card. The DVI implementation on cards that old tend to be troublesome anyway, particularly at 1920x1200 which is right at the edge of what single-link DVI can cope with, replacing it may save you some headaches in future. The thing about rewriting the EDID settings is at red-herring, at least in this case. The monitor is sending correct EDID information (mine does anyway, I can't imagine yours is any different) but the gfx card/driver either isn't reading it properly or just isn't able to set the required resolution over DVI.
You might want to try forcing 1920x1200 with the advanced timing function in
Powerstrip. It ignores any EDID-based restrictions enforced by the graphics card driver and just brute-forces whatever resolution you request. That will at least show if your FX5200 can do 1920x1200 correctly.
I use Powerstrip to set my monitor to 50Hz for TV watching purposes because the EDID information lists 60Hz as the only supported refresh rate, so the gfx card drivers don't offer anything else.