B&W 802D1 - How can I tame the brightness?

You don’t say what the rest of your gear is. 
 

b&w’s are highly revealing of components that add noise and distort highs. 

you likely need better gear especially better cables. 

EQ. Acoustic treatments. But different speakers.

@ghdprentice   I have a newly purchased pair of 22 year old Sonus Faber Cremonas and with my McIntosh 2200 amp they can still screech when fed certain cds (vinyl seems to not be a problem). The older models may have a warmer tone, but they're still honest & occasionally unforgiving, depending on the amp you've paired them with.

I can't listen to B&W diamond series at all. The tweeter's natural resonance is 35khz, breakup frequency is 17.5khz so playing anything with cymbals or bells I'll get ear fatigue (if not intense ringing) in less than 10 minutes' time.

Bright is not a word I would use to describe B&W speakers, I have sold lots of them and own a few pair, not what the OP has, the speaker is last in the chain of audio

it could be a system thing that just doesnt work, room issues, isolation issues etc

Trial and error is the only way. my take is if one cant get the sound they are looking for with basic cables like Gator cable....STOP right there. I have heard very expensive cables that just plain dont sound musical, not saying they cant

but start with the basics, try basic cables and different sources if you can and see where it goes.

Why do you say the following?

 a gross mismatch of preamp/amp and speakers.

What is this based on? any facts to support your claim?