What type number are these? If the old ones, they will be 6637 and officially were last sold in February 2007. They will have a phono plug in addition to the Powerlink sockets.
New ones, with the ICE modules, are type 6643.
Personally, I am actually a bit sceptical of the new 4000s. I think they may well use the BL4 amplifiers and this is done for economy rather than sound quality. If there was a big difference, why no big announcement? The Mk2s also need to use the mk3 Powerlink cables to prevent hum...
However I have not heard them back to back. Still waiting for an opinion on this.