803D vs 801N

They're not. The diamond tweeter and improved bass are miles better than the old 80x nautilus range of any flavor.

I own a pair of the N801's and they are an entirely different speaker than the 803. The question is more one of room size than diamond vs. non-diamond. If you room is 16x21 or larger the N801 will work fine if not go for the 803.

agreed - the D is superiour

the N is a bit dry in the upper mids, the D is neutral in this area

Go to the Abbey Road recording Studio Website. Are they using 803's? That should answer your question. They can afford whatever they wish. Are the N801D better than the N801S sure. But the N801 are far superior to the 803D's given enough space and good enough electronics.

A recording studio has far different requirements than a home's hi-fi, so be wary of the marketing.

The 801 will have a fuller sound that the 803D's won't be able to match, simply due to its size and woofer configuration. However, the diamond tweeter is far superior and lifts the overall tonal quality of the new series far above the older models.

It's really a matter of budget, availability, and (most likely) the size of your room. 801's need a huge amount of space to properly throw from that 15" woofer.