I have a CDS3. It is quite a different animal from the CDX2. It appears, on first audition, to be less dynamic than the CDX2. But, it's leading edge attack seem, to me, more natural. It sounds a lot less mechanical and artificial in this respect. Notes to to bloom into space and then decay more like they do in a live performance. But, I know a few people that prefer the more explosive attack of the CDX2.
The big difference between the two is that the CDS3 creates a much better defined soundstage, particularly front-to-back sense of depth.
My big beef with the CDS3 is that it is a bit touchy. Mine refuses to play quite a number of CDs that will play on any other machine, including other CDS3s. The Naim people are no help. They insist that those machines that are more sensitive (i.e., "selective") sound better than the less sensitive ones. Because my machine is becoming more sensitive with time, it won't be long before I can only play one disc, but it should be glorious (I hope it is NOT Nora Jones).