When testing Leap 42.2 Beta 1 I saw that Pragha is set as default application
for Music in gnome-control-center -> Details -> Default Applications. In fact,
it's the only application that shows up in the dropdown.

I guess gnome-music should be default and
/usr/share/applications/gnome-music.desktop needs some MimeType entries in
order to show up in the dropdown. Unfortunately I don't know what mime type is
needed exactly.

Site note: Despite what is set in the control center, most audio files are
opened in totem by default because they are associated so in
/usr/share/applications/gnome-mimeapps.list.