I have heard the 802 Diamond, 803 Diamond, and 804 Diamond fairly recently (within a couple of years, but before the last major tweak -- and price increase). They've almost always had the imaging "problem" but IME room treatment helps. Does not completely solve it, but they still sound awfully good to me. I always liked them reasonably close in a big room, not quite near-field but perhaps 8' - 12' (~3 m - 4 m) away. At that time the 804 sounded like it was almost a different line, nowhere near as good as the 803 or 802. A very brief listen of the latest 804 Diamond seemed to show the gap had closed.
B&W figured prominently in a lot of the testing I helped with back in the 80's. I was debating between 801's and Magnepan when I got my then and current Maggies. At that time I did some testing with my own amps that included a Phase Linear 700, Audio Research D79, and modified Hafler DH-220 plus several ARC, Krell, and ML models our store carried or I could borrow. My more recent experience has done nothing to change my opinion that, while the upper end sounds very nice with a tube amp, they need a big SS amp to show their potential. The bass just never sounded right to me with tubes, though I have never heard them with some of the big monster tube amps around now. Most recently I heard them driven by McIntosh, Classe, Rotel, and Emotiva (XPA-1, in a friend's system) amplifiers. I heard both tube and SS McIntosh amps driving the 803's and 802's. I did not care for the tube amp and my friend was able to notice the difference when we switched to SS. We still felt other amps sounded better than the Macs on them but opinions vary. I must note that, while I do not remember the exact models, the Macs were not their big new monoblock monsters but one of their lesser (albeit still very powerful!) stereo SS amps.