Just to let you know, you cannot add music to EMO. I believe that playlist you are looking at (via the EMO app) if I’m not mistaken is the EMO’s dance music that he unlocks as grows older.
Currently there is no plans on adding custom music into EMO so he can play it. The music EMO can play is the music associated to the when you ask him to Dance. And older he gets the more dance moves / music associated to that new dance move he unlocks.
If you want to see more info about this, feel free to take a look at my EMO Guide that explains EMO’s dance music and other info that might come in handy for new EMO owners.