Default Music Player

[Biker Dude1]

I have a program called Music Auto Play, which starts my default music player every time headphones are put in the jack or a bluetooth music player is connected. I use Google Play Music but, for some reason, the 'Music' application always comes on and starts playing so I have to open the phone and change from that program to Google Play Music. I went into default applications and there is no default set. However, I cannot figure out how I can just make Google Play Music the default music player.

Any help on this would be appreciated.