I have an appletv3 with the HDMI connected to a TV and the optical connected to a 5.1 receiver. I have my dolby digital setting set to "auto" When I play a movie with a 2channel AAC track and a secondary 5.1 AC3 track it automatically defaults to the 2 channel. If I set it to "on" it uses the AC3 track and goes to my receiver. Is this the correct behavior for the "auto" setting? I thought it would detect the optical and default to 5.1