Just tried out the "ConnectedMonitor" option: when applying "CRT",
then the X-server tells that the pixel clock limit is 400MHz (otherwise
it says 330 MHz). My LCDs couldn't receive any signals through DVI,
but I guess that's to be expected :-)
So in your case this might help
Option "ConnectedMonitor" "DFP,CRT"
Assuming your small display is the first device connected through DVI
and the Barco is the second device connected through VGA.
Then the modeline of posting #19 (derived from the timing information
you provided in posting #18) should also work. If not, then I guess
it is necessary to define a metamode for your display combo.