What you've said is completely accurate. The crackling problem is, IMHO, a "bug" and shouldn't be normal or expected, but otherwise everything you've said is true.

It's leaving out one important detail, though:

Most of the things that audiophiles would notice about the differences between DACs, and the differences between digital and analog connections in that situation, are very subtle and usually involve very high frequencies. It's these very subtleties that are affected by MP3 lossy data compression. So in the case of the Rio Receiver and Rio Central, it's all more or less moot.