Borresen speakers are designed to compensate for our ear’s lack of sensitivity at lower volumes. They measure poorly by textbook standards but they sound dynamic and satisfying at the loudness levels most listeners prefer.
The primary complaint I have with B&W’s 800 series is they lack the bass drive and fullness you’d expect from a speaker of their respective size and woofer complements, which is especially true of the 804s and 803s, much less so the big 800s. I have never found the 800 series to lack any “sparkle” or detail in the highs. Their diamond tweeter is one of the best in existence.
Alternatively, perhaps a better and cheaper option vs new speakers would be to invest in expertly designed room treatments, especially with regard to the high frequencies.