Re: tripple monitor setup
These quotes are from the README for the latest NVidia driver, maybe you should check in with the Xinerama developers.
o Both display devices share one frame buffer. Thus, all the
the functionality present on a single display (e.g. accelerated
OpenGL) is available on TwinView.
OpenGL + Xinerama
Currently, OpenGL will not display to anything other than the
first head in a Xinerama environment.