Make Shuttle default MP3 app when using Moto Voice

[MarkSBaines]

If I ask my phone to play some music, say "OK Moto X play some Marillion" it does a Google search then plays a random MP3 file in my Music folder using Google Play Music.
OK, very smart, but I have and prefer Shuttle music player.
So how do I get Shuttle to be the default MP3 player in this situation?
In a file explorer I have set Shuttle as the default app for MP3 files but when using Moto Voice it still starts up Google Play Music.

 

[MarkSBaines]

Found a solution but it isn't a permanent change.
When Google search comes up and starts playing the music, showing the Google Play Music icon top right, there is a hamburger you can select and then choose the music app of choice.
Simple when you know how but not very intuitive. Would have been nice to have been asked the first time which app to use, like everywhere else.