Just installed a 2nd nvidia video card -- previously had gnome 3 working perfectly with 2 monitors on a a single video card using twinview

tried a number of things thus far

• twinview on 1 card + xinerama
• no xinerama no twinview
• various manual xorg.conf hacks based on random forums (couple references below)
• xinerama no twinview with and without Extensions Composite

The last one is what I'm using now -- it results in a forced fallback mode with Composite Disable set at the end of xorg.conf via nvidia-settings

Section "Extensions"
    Option         "Composite" "Disable"
EndSection

when I disabled that last snippet it boots to gnome 3 full with the left monitor on a black screen and the middle monitor as primary but non-responsive switching to console mode Ctrl+Alt+F1 and then switching back I get 3 black screens with a mouse that can move around but nothing to interact with

issue seems related to OpenGL and the multiple video cards -- I can boot into Unity without issue though my Glx-Dock shows up with the black background as barely shows in the screenshot below indicating the OpenGL is not initiated

has anyone had any luck with getting Xinerama to work with Multiple NVidia Video Cards with OpenGL support?

Found this in the logs while looking a bit further

[    23.208] (II) NVIDIA(1): Setting mode "nvidia-auto-select+0+0"
[    23.254] (WW) NVIDIA(1): The GPU driving screen 1 is incompatible with the rest of the
[    23.254] (WW) NVIDIA(1):     GPUs composing the desktop.  OpenGL rendering will be
[    23.254] (WW) NVIDIA(1):     disabled on screen 1.
[    23.277] (==) NVIDIA(1): Disabling shared memory pixmaps
[    23.277] (==) NVIDIA(1): Backing store disabled
[    23.277] (==) NVIDIA(1): Silken mouse enabled
[    23.277] (==) NVIDIA(1): DPMS enabled

According to this page at the NVidia User Docs

• http://us.download.nvidia.com/XFree86/Linux-x86/173.14.09/README/chapter-14.html

I may be out of luck =(

Starting this question with the hopes that others may be able to help debug and perhaps gain answers over time as I really want to get the full gnome 3 back.