I believe the issue has to do with one of the monitors using the Displayport because I have the exact same problem using a GTX 680 and 3 BenQ XL2420T monitors. They all run fine at 1920x1080 at 120Hz when they're not set to surround mode. When I try to enable surround, the max resolution it will offer is 3840x1024 at 75Hz or 4320x900 at 120Hz. So, related to what Bifurk8 pointed out, even though my monitors are identical models, the fact that one is connected using the displayport causes it to use a different sync polarity. In my case, the monitor on DP is (+,+) and the two on DVI are (+,-) and so the surround res is being forced lower than native. I have tried switching which one is using the DP cable and the polarity stays the same in regards to the cable, not the specific monitor (in other words the monitors don't care which polarity is needed, it will use whatever the connection type requires.) If I try to force the polarities to be the same before enabling surround, it either doesn't change at all or it flips to the exact opposite (+,+ to -,- or +,- to -,+).
I have made a few posts about the issue on the nVidia forums and not gotten a direct response to any of them. Hopefully they are aware of the problem and working on it even if they aren't specifically saying so. Interestingly, somewhere on nVidia's site it says that with future drivers they will support 3D surround on one GPU, but only using the XL2420T, presumably because it is one of, if not the only, monitor out currently that supports 120Hz over the displayport (120Hz being a requirement for 3D and HDMI only going up to 60Hz). So for them to already state that possibility up front, they must believe that it is possible to enable surround in a DVI,DVI,DP configuration at native resolution and frequency. The only question is do they think it should already be working currently in 2D mode and just plan to add 3D support later, or do they know that any surround in this setup is currently broken and plan to fix it in future drivers? I just wish I could get some sort of official response on the matter.
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