British magazine Sound On Sound published an extensive review of CS2x (and compared it to CS1x of course too) in their march issue.
Here's their web site:
http://www.sospubs.co.uk/html/home.htm
although I think you've got to be a subscriber to read it online.
It sounds like among other things CS2x has new better sounds, better arpeggiator and is backward compatible with CS1x (can transfer CS1x sounds to CS2x).