Great work! I use and follow this project (osmc) since it’s beginning.
I’m a big fan of what you guys are doing here!! 
I tested my self this feature with an old usb dongle… it’s kind of slow, it has some delays, maybe because is not BT 4.0.
Is there any chance to have this running with PI3 BT driver that is in development ?
It would be nice to use the built-in pi3 BT for A2DP 