[noggin]

In the U.S., with the few BD's I've seen, it's ATMOS + TrueHD + core. In EU, it seems some have DD+, but in place of what? TrueHD? I'd expect if a user's AVR doesn't support ATMOS, it would output as TrueHD (as in my case), and then if no HD audio, as core DD5.1. Basically, I'd expect there to be backwards compatibility or fallbacks that work, but just guessing.

European releases are often original sound track in Lossless, foreign dubs in high-quality lossy (though sometimes there is also a Lossless French or German track). I think the same is true for Atmos releases.

OST in True HD with Atmos, additional language dubs in DD+ with Atmos. (There isn't the bandwith required for multiple True HD tracks)

These DD+ with Atmos tracks are separate tracks with different audio and not related to True HD trakcs. The question is whether DD+ with Atmos tracks are output as : DD, DD+ or DD+ with Atmos.