Why are my B&W 803D speaks feel bright

I have Meridian 605 amps and don't find them bright. I have had several B&W speakers but not the latest generations. You may be having room problems but a simple thing to try is along the lines that Rwware suggested. Go to an office supply store and get a laser pointer; put a tall narrow object like a lamp just in front of your listening position; then fasten the laser pointer onto the speaker with masking tape of blutak so that it points straight ahead. Use the laser pointer to align the speaker so that it hits the lamp directly. Do the same with the other speaker; now the axis of the tweeters are crossing directly in front of the listening position. This alignment was developed by the BBC in the early days of Stereo and is known as "Hugh Brittany Angling" after its developer. Does NOT work with every speaker but will with most. I just thought I had my Spendor S 100s aligned correctly by eye but kept getting too bright a sound. After I had used the laser [ which I should have done first] the sound was noticeably softer but actually had more treble detail. I got the laser pointer idea from the Wilson set up guys who installed my friends Sasha.

Def try a tube preamp, I have B&W Matrix 802's Classe amp and ARC LS-7 Match made in Heaven. Never harsh or edgy. Ditch the rotel.

Mac 402 or 501s work very nicely with the 803ds.

The only way to properly determine the exact cause of your issue is through experimentation. But good insight before you do never hurts.

Most of the B&W speakers I had an opportunity to listen were forward in their presentation. I fortunately have heard the 803D and 802D. They were not in the same system so I can not provide a proper comparison between the two. My impression didn't have any notion of brightness, but its presentation has a forward presence that might not mate well with some components (particularly ones that have been described in a similar way). I have heard people using Classe with excellent results and my best experience with them was paired with Naim. Another setup I heard with the 803D was surprisingly lifeless. I had forgotten what the rig was, mostly because it didn't really leave great impression.

BTW, could you provide a more detailed description of the room and speaker setup. It could greatly affect the bass performance and thus make the balance all wrong. With a speaker such as yours, system synergy and setup are two very big factors. I personally have not heard any of your gear in any system so I can not comment on them.

Almost any speaker can be made to sound good or bad depending on set up.