Vega,
Having a look it seems the BNC connection is a one way connection, whereas VGA is a two-way hence getting the EDID back.
Found this link http://msdn.microsoft.com/en-us/windows/hardware/gg487330 deals with overriding the EDID info via an INF file, now I know you said you looked about masking it so not sure if you have tried this yet.
Either way hope it is of some help
Kimbie
Ya, whenever I try and mask or override the EDID it would not put my 3x FW900 in Surround. Only when I let the cards physically talk to the monitors would it allow Surround. I think nVidia made it this way to be super cautious as to getting Surround to work properly. I play to trick the ******** with EDID emulator hardware though!