None of that remotely answers the question.Stereo on their TV's speakers, with their Xbox (and the game itself) likely set to surround, since most people probably don't care enough to change the settings to match appropriately for their setup.
The Xbox will upmix everything to Atmos if you tell it to, or it will pass 5.1 or 7.1, or stereo. It has to be set to Atmos to get the actual Atmos output, and your receiver has to decode it, which in turn, maps the sound to however many speakers you have, and wherever you put them.