I've heard both the 800D, 802D, and 803D. I've also heard the 800N and 801N. To my mind, the re-design incorporating the diamond tweeter makes the newer 'D' versions a considerably better speaker. I found the overall sound presentation to be more of a piece with the D than its predecessor, and the upper frequencies are incredibly clean and distortion free, so much so that I didn't hear the tweeters at all (this is very rare and the sign of a really good tweeter IMO). I found the music has an added sense of naturalness and realism with the D version. The presentation also sounded less strained to me.
Make sure you here the D version after proper break-in. After having the 'before' and 'after' results with the 800D specifically, I found it really does make a difference.
I would have to disagree with Missioncoonery. I find that the 800D is a superb loudspeaker.