How to keep audio players from starting automatically upon reconnecting to a bluetooth device? Galaxy S4, 5.0.1

How is the system determining which audio app to use when reconnecting to a bluetooth device? Is there a way to change it?

I downloaded some MP3s that won't work in the Google Play Music App, nor Amazon Music app for whatever reason. So I gave up, and decided to play a podcast using a podcast app. Then I connected to my car's bluetooth stereo, and even though the podcast app was open and playing, it tries to use Amazon Music to play the last unplayable MP3 I tried in it. It fails, giving me an annoying notification.

This happens even if I close Amazon Music from the task manager. It still keeps opening back up and trying to play music when connecting via bluetooth, it's like my phone does not have my podcast app recognized as a playback app if Amazon Music (or Google Play Music) apps have been opened since the last phone boot. They seem to have priority over it.

Is there anyway to change how this 'last music app' is triggered or configured?
Due to poor development with some phones, most music apps will still be running in a background process even after you close it. 

My advice is to use an app called "Purify". Unlike most task managers, this app keeps app processes closed after you close the app.

But be aware that Purify can temper with many of your social media apps and you may not be able to receive notifications from Facebook or Instagram after you close the apps.

Purify SHOULD be able to prevent your audio player from automatically opening when connecting bluetooth.

Also, it works BEST on a ROOTED device.

If it doesn't work, let me know!