From my point of view. You can not play the audio on the xbox in the background. Because, when you are playing games you can hear only gaming sounds. Game sounds are important thing while playing the game. You can enhancing best experience while playing games.
Yesterday, the Xbox One was shown in the ‘stream to’ section. When this is the case, yes you can have background play. Whereas today, for an unknown reason, it’s not available to stream to, thus no background play.