To use Separate App Sound on a Samsung Galaxy phone, go to Settings > Sounds and Vibration > Separate App Sound, toggle it on, choose the app (e.g., Spotify), and select the audio device (e.g., ...
I have mediocre computer speakers on my desk, and a nice stereo way across the room. I'd love to be able to send audio from mp3s, pandora, and other music to the stereo, while having "windows sounds" ...