How to set default Programs for media files?
On Windows and OS X only the OS registered application is used.
On other OS you need to add/change the values in your phexCorePrefs.properties (
found here):
SystemTools.OpenVideoCmdOtherOS = xterm -e mplayer %filepath%
SystemTools.OpenImageCmdOtherOS = ee %filepath%
SystemTools.OpenAudioCmdOtherOS = xterm -e mplayer %filepath%
SystemTools.OpenBrowserCmdOtherOS = mozilla -remote openURL(%filepath%,new-window)