I've just downloaded a song into my LG90 phone and it plays on my system.
When the system connects to your phone and say's connected, press the media button and it should find song's on your phone, if it doesn't go to settings in your system, touch the on screen "bluetooth" icon , go to the top icon "view device list" click on that and a screen will pop up with the name of your phone, click on that and another message will pop up and say "do you want to connect to phone.
Now sometimes it will automatically show your song list and start playing or it will go to the phones keypad screen, if it goes to the keypad screen just press the "media" button again and it should work. I did have the song playing through one of my apps on the phone not in a file folder so I don't know if this makes a difference.