I had a Sennheiser BT T100 Bluetooth transmitter hooked up to my LG TV because the TV's Bluetooth was pretty weak. It worked out of the box. Plug in a toslink cable between TV and transmitter and it just worked. I wanted to do the same with my Xiaomi MiBox S (4K) but I get no audio out over its mini toslink. Light's on but nobody home.

FIX: I happen to have two MiBoxes. When I tried the other one, the optical works without any setup. Either the first MiBox is broken or the other is another model, which is certainly possible. The one that works has a white LED shining from between the grille on the front, and its remote has buttons for Netflix and Prime Video. The one that doesn't work has no light on the front and has a button for Netflix and, I think, Google Play Video.