How can you tell if an SACD you are buying has multi channel capabilities or is simply 2 channel sound? If some of my existing cd collection were released in multi channel then I would be tempted to replace them but not if they were just 2 channel I (even though they do sound better).
There's usually some information on the disc that tells you the format, though it may be a little obscure.
You could also try checking here; click "links" then "release list". Unfortunately it's not in alaphbetical order and can be a little out of date. For new releases try here and here.