DSP ? or send one to Danny @ GR research he can fix them  see if he allready has a fix for that speaker? i just watched 2 YT vids about him fixing a pair of $27.5 K Wilson watt puppies! wow $27 K and they are real POS needing a LOT of re-work to be optimized!  weird! 2 part YT video! 
https://youtu.be/Tma9jFZ3-3k?si=GcgkV3o2Ep5KvSaA
https://youtu.be/pIt2pcQvf6M?si=V-nu0XtiWsQXfQlx
his kit for B& W is   
https://youtu.be/wmmw8QlThPk?si=Svwa4ln20v7rZkVn
only 54 parts! needed a lot of fixing ! LOL 

B&W 802 S2 Upgrade Kit (Pair)

$525.00–$692.00

The price is per pair.

This upgrade kit fixes a number of issues and greatly improves the quality of the crossover over the stock network.

The kit includes all of the necessary crossover parts, along with wire, solder, heat shrink and a set of tube connectors.
A new crossover/mounting board is not included.

Bass-Alignment Filter: B&W’s “bass-alignment filter” is compatible with our upgrade, as it only addresses frequencies below 100Hz. however we do not recommend it as it is more of a “band-aid” than an actual fix for poor room acoustics, while also robbing clarity from the midrange and treble.

I think you should replace the speakers or you spend all of your time acquiring components, etc to counter a specific deficiency. 

B&W upgrade kits….

These speakers and all the tweaks offered by other forum members (and now upgrade kits) suggests there are just some flaws with the design. Is this tweaking and upgrade path normal with speakers?

Are the 802’s (for example) the equivalent of the original Linn turntable that requires (in most cases) constant upgrades or fettling to please their owners?
Just adding the simile because the Linn comparison evidence is out there for all to see, and often on this forum.

Saying that, l have never heard of so much frustration or irritation with any specific model of speaker before. Every brand l have ever bought has never needed to be rewired or altered unless cosmetic repair or treatment was required.

I would just trade or sell these B&W’s on if they are that bad, but for me an audition first would have avoided all the fuss. Throwing more money at electronics is not always the best option.

There are many types of speakers which can be overly bright; ribbons, horns, etc….. 

One thing to consider is parametric equalization (PEQ) or low pass filters applied in the digital domain before your DAC.
Additionally it's desirable if you can achieve a "Harman tilt" or "Harman target curve" for a more enjoyable listening experience.

We have a video which overviews one way of doing using miniDSP Device Console  
 

@onehorsepony, 

I had the same issue with the entire B&W 800 series line and ended up purchasing Aerial Acoustics some 30 years back and been there ever since.

I would check into other speaker lines and if possible check in room for audition.

Good luck and happy listening!

DeeCee