Next step after B&W 802D

Your amp speaker combo is a mismatch. You either need a 200 wpc plus solid state amp or speakers that can be driven by your 50 wpc tube amp IMO.

Sean

Depending on your musical preference:

Airy and holographic - Elac with mushroom head, Venture
Holographic with more weight - MBL 111 or 101
Razor sharp with details - Usher BE10/20
Pleasant with details - Analysis (forgot the model)
Dynamic & musical - Avantgarde Duo or above

I had the B&W 802 (non diamond) and went to the Wilson Sophia 2. The Sophia 2 is a great speaker. I'm now using Dynaudio C2 but I still prefer the Sophia to the C2 and the B&W 802. Agree with Bar81, see what you want to improve on. I wanted to improve on the bass and I couldn't get Bass from the B&W 802 because I was on the 2nd floor with cheap floor boards and I think the downward firing bass just went down stairs. My friend put them on concrete and they sounded completely different with much better bass.

With your amp, its not enough to drive the N802 as many here aired out.
I think your amp would work better with the Sophia 2 Or get one of those solid state amp from Accuphase and it will drive your N802 well.

Maybe you should try (more?)room treatments at the 1st reflection points before changing any components. Those bare walls(pic have got to seriously affect imaging, soundstage, clarity, etc.

Proper treatment might even raise the performance of your system, overall, to the point that a speaker change is not necessary.