Why are my B&W 803D speaks feel bright

Years ago I sold Levinson, Rotel, B&W, Magnepan, Thiel, and other brands back in 87-89. B&W's are not bright by any stretch. Thiels to me back then were. I agree with the previous post, try a different preamp. Rotel is good, but not in the same category as your B&W's. B&W's are also fairly power hungry as I recall.
Back then, when I sold a complete system, I tried to keep all components within 10-20% in cost relative to one another. Think of the 'weak link in a chain school of thought'

Don't know much about the cd player you have. Hope that helps.

AQ cables are not helping you. For starters, get sth on the warmer side - Cardas Golder Reference cables, van den Hul The Revelation/The Revolution or similar.

B&W designs them this way.

move them around.

Rotel and B&W used to be imported by the same distributor so they were almost always sold at the same stores. Therefore they usually ended up together.
But if you want to tone them down, without spending any money, toe them in to where the tweeters cross in front of your listening position. You will probably want to spread them further apart if toeing them. Toeing them in will also give you more depth and center fill.
If it doesn't help, you've only spent a little time.