Hello all,
Wellcome to VOX support forum.
Vladislav, Apple fixed many issues with Bluetooth devices since El Capitan. Almost in every update notes Bluetooth devices were mentioned.
Two things you should mind concerning Bluetooth speakers:
1. Not all types of playback controls are supported by VOX as longs as we are not able to test it with each and every control.
2. VOX jumps to the built-in audio interface if external or Bluetooth device becames unavailable. It was done on purpose. Otherwise, you'll be seeing the playback progress without any sound.
I hope this information helps. Have a great day/night!