I still stand by my comment before that when you play the disc live and decode with an Atmos-equppied reciever, the actual Atmos audio stream is somehow adaptive to however many speakers are in your setup. The question is how many discrete channels were used when they actually mixed this title in the studio.
That's my (rather fuzzy) understanding, too. From the explanations I've read, all of the "object placement" information is metadata, and in playback, Dolby's magic algorithms "place" the object information differently according to how many (and what type of) speakers you have. If you have fewer speakers, then they rely more on psychoacoustics than on discrete placement. But I think there are still 7.1 (or, as new member @hotRocks1061977 claims above, 5.1.2) "discrete" channels in the core.
My question is: how do you "rip" the metadata along with the music? And to what file formats? The only commercial download of an Atmos recording I know of (so far) is John Luther Adams's Become Desert, sold by Acoustic Sounds, and the label head told me that the only format it could be offered in was mp4. (I got the impression that Dolby dictated this, though I'm not sure.) Meanwhile, the Atmos test tracks that Dolby makes available on the web are mp3s, whereas the "upmixed" Atmos tracks that Glenn (zeeround) was offering for purposes of comparison a week or so ago are wavs.