When there's no singers autokdj can play your filler music, then automatically switch back when your first singer enters the list.

Make sure you have "Start playlist upon first karaoke enqueue enabled.

Click on Add file, or add dir, or add url (for internet radio stations)  Add some stuff to the playlist.

From the autOKdj playlist view, highlight all the songs, right click, then select "Mark this song as Lowest Priority".  You can hit play on one of your songs now.

autOKdj will play your lo priority playlist until your first karaoke enque, then automatically switch to the karaoke song. All your lo-pri songs will remain at the bottom of the playlist automatically,  karaoke singers are placed ahead of this lo-pri block of items on the playlist automatically.