Switch music apps depending on bluetooth connection (car/headphones)
I found a fix. 

The app Macrodroid allows the user to create very simple but effective logic in automating which app is opened depending on what Bluetooth device is connected. 

Also, after trying a plethora of music apps (Poweramp, PlayerPro, RocketPlayer) I found that Samsung Music allows my car to display all folders appropriately. I also found that Samsung Music stores the music quite simply and has a great EQ to boost quality. 

I still use iSyncr to send playlists to the /Music/ folder on my SD card. So in short a combination of:

iSyncr + Macrodroid + Samsung Music


allows me to seamlessly control where and how my music is played.