Following-up this discussion at the MB Style ML: http://musicbrainz.1054305.n4.nabble.com/How-to-enter-hybrid-SACD-and-DVD-audio-video-discs-td4669680i20.html I propose a clarification of the guidelines concerning hybrid SACDs:

• the CD layer of the hybrid SACD shall be represented by one medium
• the tracklist shall match the DiscID of the CD layer
• the medium title shall be "CD" for untitled discs or "<disc title>: CD" for titled discs
• the SACD layer of the hybrid SACD shall be represented by a separate medium
• stereo and multichannel audio shall be represented by separate recordings
• the tracklist shall include separate tracks for all pieces of stereo and multichannel audio
• a format ETI like " (5.1 mix)" shall be added to the track titles of the multichannel audio tracks
• the same format ETI shall be added to the disambiguation comment of the multichannel audio recordings
• the medium title shall be "SACD" for untitled discs or "<disc title>: SACD" for titled discs