Just a small point on your use of the word "layer" in this context.
The multichannel mix and the stereo/mono mix occupy the same hirez layer - just on different areas. When the SACD loads you can select either area. On my player (probably on all players) you can specify the default section you wish the player to seek to initially, so if you are just into stereo (as I am) just set this up correctly and you won't even know you have m/c discs.
If the disc is a hybrid, then there is another layer - for the Redbook encoding.
The multichannel mix and the stereo/mono mix occupy the same hirez layer - just on different areas. When the SACD loads you can select either area. On my player (probably on all players) you can specify the default section you wish the player to seek to initially, so if you are just into stereo (as I am) just set this up correctly and you won't even know you have m/c discs.
If the disc is a hybrid, then there is another layer - for the Redbook encoding.