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

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?

Nah, just a WAG based on your description of the sound you are getting, i.e. too bright and poor bass, etc. If my use of the word 'gross' offends you (and it must since you seem not to focus on any of my other posts) then I will gladly admit it was probably a superlative and change it to 'minor'. That help?

IF the speakers are properly set up in your room, something that was suggested in many posts in your 2 threads, by myself and others, IF the electronics are high quality and 'matched' properly, then, the only thing left is the speakers which must be deficient for your purposes. If the speakers are not deficient for your purposes then you really have a conundrum. Good luck solving it. 

B&W speakers with the diamond tweeter are very bright to my ears. The solution is to use a warm preamp and amp combo. A number of years ago I heard one of the larger pair at Best Buy Magnolia with a Rotel preamp and amp that sounded very good. The very reasonably priced Rotel components actually sounded better than the pairing with high priced Mac tube monoblocks. B&W and Rotel are closely aligned companies, and B&W has been known to voice their speakers with Rotel components. If there is a store near you I would call them and see if they have the pairing for a demo. Costs you nothing to hear for yourself.

B&W speakers with the diamond tweeter are very bright to my ears. The solution is to use a warm preamp and amp combo. A number of years ago I heard one of the larger pair at Best Buy Magnolia with a Rotel preamp and amp that sounded very good. The very reasonably priced Rotel components actually sounded better than the pairing with high priced Mac tube monoblocks. B&W and Rotel are closely aligned companies, and B&W has been known to voice their speakers with Rotel components. If there is a store near you I would call them and see if they have the pairing for a demo. Costs you nothing to hear for yourself.

Stay away from noisy graphic EQs and get a Schiit Loki. Four bands, under $200.

Steve Guttenberg has one and loves his.