Displays ... again ...

CentOS 7 current, TDE current. Nvidia Quadro M2000 (4 x DP out), 2 x Dell P2416D displays. Applied patches last week and one of them (that seemed to be related to the Nvidia proprietary drivers) blew up the system. Eventually ended up re-installing in an ultimately-failed bid to get productive again (this is my work system). Decided to forgo the Nvidia drivers and use the open source stuff. Xrandr is a nightmare though, so I thought "well, just use the TDE built-in screen controls". Problem is that System Settings -> Monitor & Display can only see one of the displays. How do I get it to see the 2nd display? Yes, it's plugged in. Yes, I've checked "Enable global display control". Yes, I've clicked "Rescan Displays" (many times). "Test Settings" gets me "xrandr: Failed to get size of gamma for output default". Not sure the system is seeing the first display correctly even though it's working (I am typing this message on it) because while is sees 2560 x 1440 pixel, it thinks the refresh rate is 0 Hz (though, again, its working). Do I have to create and edit an Xorg.conf? Because I tried that and it didn't go well not to mention defeating the purpose of a "settings" GUI ... -- Peter Laws, BS, MRCP / N5UWY National Weather Center / Network Operations Center University of Oklahoma Information Technology plaws(a)ou.edu