If you did an ordinary HD install, some of the autodetection and adaptation faculties of Knoppix may have been reduced. I don't know how it is now, but I experienced something of that with HD installs of Knoppix5.X. In your situation, apart from doing a poor man's install and running from that, I think I would have checked Ubuntu, Mandriva and possible other live distros, and if they tackled the external monitor problems, I would have tried to find out how they did it. It may have to do both with hardware detection, module loading and Xorg configuration. And my experience is that Knoppix now, generally, needs to have the external monitor resolution specified at bootup.