The Register heeft wat info over Diamond's Rio. Het ding ondersteund nu ook Liquid Audio:
The big difference between Liquid Tracks and MP3 is that for former includes mechanisms to support licensing music tracks to individuals. That ensures the artist and label get their cut of the sale and that the licensee can't copy the track for others to use.
It's the lack of these features in MP3 that has had the music industry up in arms against both the format and systems, such as the Rio, that encourage its use. Liquid Tracks is one of the formats the music industry sponsored Standard Digital Music Inititiative (SDMI) is considering as the basis for a new, universal digital music format.