Can't get the file associations to work

[Virtual]

I didn't do any file associations during the install.

I have found the file association page in preferences (see picture).  But how to operate it?  There are no check boxes for the file types you want to associate.  So, you must associate all of them at once or none, correct?

I seem to have associated ".mp3" files (and all the rest, I guess).
 
However, nothing I do will release my ".pls" playlists from the grasp of Winamp over to AIMP.

[Soolo]

Button "File Types"