Thanks, it appears that is also true for the VGA port. As long as something is plugged into the VGA port, the DVI configuration is ignored. This is really confusing, as KDM still functions on that monitor, and then the X-Server ignores the configuration, even one that does configure X to use the DVI output.
However, all this only pertains to the X-Server. I got the DVI now working as the only monitor for KDM and X-Server, but I still can't see the console output, before X-Server is even started. Any idea how to get that directed to the DVI output?