Re: Dual/Single Link TMDS
as a not very elegant workaround, you could save the EDID of the DFP in a file while it is directly connected to the Quadro, using nvidia-settings. Then use the xorg.conf option to load that EDID from the file rather than getting it directly from the connected hardware while the switch is connected. It worked for me but there is a recent forum thread which discusses situations where saved EDIDs in a file were rejected by the driver as well.
I had a somewhat related problem. I first tried to reconstruct a modeline from the working EDID and the verbose log but in the end was only be able to use an analog connection with such a custom modeline.
Hope this helps,