Denon PMA 2000R v 2000RIV Whats the difference?

Question on the Denon PMA 2000R v 2000RIV. I have had the 2000R and found it to be a great amp but as some (including reviewers) have pointed out it can be a little soft, dark and sound somewhat unexciting. Is the latest version , the 2000RIV any different in its sound?? Has anyone compared them?? I know the later weighs 10lbs more . Thanks,KG