The backend playersTable of Contents
KMPlayer uses external programs to do the actual playing.
There is a configuration tab for MPlayer in KMPlayer's config dialog. Here you can set MPlayer's path and it cache size for network stream, among other things.
This player configuration name is mplayer.
The best way to debug this backend is to start KMPlayer from a console application like konsole. Then start a movie with KMPlayer and see the exact commandline that is used to start mplayer in the console application. Now copy/paste that to another console, remove the '-wid 12344' options, and make it play. Probably it's just choosing the right -ao/-vo params. Also make sure mplayer doesn't start default with a GUI.
Another debugging tool is the 'console' button in KMPlayer's toolbar. Here you can see the output from mplayer.