BTW.: the xorg.conf above provides just one big screen. Since you have a
"seamless" display array, I guess that's ok for you. However in case you need
to sub-divide the display array into logical screens, then just add the following
lines to the screen section of your xorg.conf.
Option "TwinviewXineramaInfo" "True"
Option "TwinViewXineramaInfoOverride" "1024x768+0+0, 1024x768+1024+0, 1024x768+2048+0, 1024x768+0+768, 1024x768+1024+768, 1024x768+2048+768"