Internally for the sources, KMPlayer uses distinct names. At the time of this writing these are "dvdnavsource", "dvdsource", "exitsource", "introsource", "pipesource", "tvscanner", "tvsource", "urlsource", "vcdsource" and "vdrsource". When activated, they mostly starts playing the list of playable items.

You can activate a particular source with a kmplayer:// type URL. Just set the host part as the source name and optional path part as extra arguments, so for a channel for the "vdrsource" this could look like kmplayer://vdrsource/22 MTV 2. Eg. this script starts KMPlayer using "dvdnavsource" and using D-Bus to play fullscreen.

/bin/bash
kmplayer kmplayer://dvdnavsource/ &
PID=$!
sleep 2
qdbus org.kde.kmplayer-$PID /kmplayer/MainWindow_1 showFullScreen
    

For some sources this will not do much because they are not meant to be for normal playing. For "pipesource" this is disabled because that would be a bad security hole of course.