No clue about that jack. Wild guessing, if Nvidia monitors temp like Intel, then the sensing is on chip but still requires a device nearby as the interface. I think that may be missing on this board. But, I have never plugged one of my M2090s in as I just have not had the time. I have had a i7-990X for several months to upgrade from a i7-920. I am hoping to be able to do the upgrades in 1 weekend.
I think the jack for the fan is in the opposite corner ... where there is no jack but a place for one.
If you are in CUDA mode for most of your analysis running 25% CPU load, why upgrade the processor? Just curious.