802 diamonds with class d amp

I can't speak to class D amp options having no familiarity with them. I have B&W 804 Diamonds (the current 2nd gen) and use Musical Fidelity's M6PRE (class A) and M6PRX (class A/B, 260w dual mono) which pair nicely with 804 Diamonds and didn't put me in debtor's prison. MF makes an M6 500w integrated that lists new for $7000. I suspect it would work well with 802 Diamonds. There are a couple of M6 500i demo units listed on Agon right now both under $5k. Just a thought. I have no connection with either seller.

I don't seem to have the depth issue you indicate. What sound differences will I notice with a better amp?

You first have to understand what the differences are between the talents/properties of a Rotel and a Pass Labs for example. Also the difference between how wide and deep a speaker can make the stage. Because B&W does not make crossovers what can give you an exeptional deep and wide stage. Like Musical Fidelity ( I owned it, sold it for a long time and I even did audio shows for Musical Fidelity) is not very good at giving a deep stage. There is only a little of depth. Every brand even if you are talking about an amp, source or speaker have there own properties/talents. There is a very big difference in how the stage is projected between all these brands.

With the B&W and Musical Fidelity components that I'm using and given their price points, soundstage width and depth is acceptable but definitely not exceptional. For me, the ability to reproduce the sound of different instruments with realism and clarity across high, mid, and low frequencies is a more important consideration than soundstage width and depth. In these areas the B&W and MF components I'm using are exceptional given their price points. Certainly if I could afford Pass Labs amplification, I'd be waving goodbye to MF and using something else.

B&W with MF is a very good combo. Both miss the most important part in highend audio. This is depth and playing even beside your speakers. MF also makes expensive amps these days. Compared to brands Like Pass Labs there is still a lot missing. This is not only in de way a stage is build. But also in sound realism.