Hi Audphile1,
Certainly there can be numerous reasons why we differ on our impressions on the 803D. It can be gear,cable, or room related. However, my observations were derived from listening to the B&W 803D, N802,and 802D at the same dealer showroom, driven with the same gear and same cables on the same day with the same music cds that I brought. This paints a really accurate picture in relative comparison of all three models, so I was able to pinpoint each one's attributes.
From what I have found, the N802 was the most laid back of the three, and second was the 802D. The 803D was the most upfront sounding of the three models. Not saying the 803D is up in your face type of forward sound, but compared to the other two B&W models it was. This observation is consistent, because the diamond tweeter, though non fatiguing, does bring the presentation a few rows up front more than the older N802 (not the N803 or lower models). It also is consistent that the 802D , due to it's separate Marlan midrange design, was a little more laid back than the 803D design.
But I do have to agree with you that the Nautilus 800 series' tweeters can (at times) sound not as smooth and a little uncontrolled/harsh if upstream gear, or cables, or cds are not mated well.
The best of both worlds would be the 802D, because it has the qualities of the new 803D, yet have some resemblence of the older N802. But if one has to choose between the 803D or the N802, it's a matter of preference more than anything else. Each plays music differently, whether one is better is hard to say, it depends who you ask and what their preference is. You can't go wrong with either.