What is wrong with my system?

i agree with @yogiboy

I hate to burst your bubble but any B&W that I have listened to are bright.

given the words of fairly extreme frustration expressed by the op on the sound he is hearing, maybe the best bet would be to get a set of warmer, more tonally balanced speakers like harbeths or spendors or vandersteens

...of course, after confirming his speaker set up and room are ok...

Your equipment seems to be ok as you noted.
Try changing your cables. I’ve had good sound with my 801’s using Kimber cable in my second system.

A tube preamp is the economic choice for you system. You have nice stuff, it just isn’t working together. No need to dump it all or the expensive pieces, a nice warm tube preamp will do the job. personally I would not go with Audio Research for your system, more like a Cary SLP-98.

The challenge is that this are bright speakers with components that are not warm enough to offset the bright speakers. There is nothing inherently bad about a bright speaker.  It just needs the right equipment to balance it out.  Many elite speakers are on the bright side of the spectrum.  
You can do a few different things. You can add treatment.  An overdamped room will suck the brightness out of the system.  You can change speakers.  Vandersteen would do the job as an alternative or you can change equipment.  
My hunch is preamp and DAC would be the obvious first swaps.  A warmer preamp and a warmer DAC can do wonders.  
There is no silver bullet one component.  I would make a single change and then reevaluate.  
One other thing.  Power conditioning does matter and have no a decent power conditioner can smooth things out a bit.  I would also be curious what cables you are using.

Also, are the speaker cables coiled at all.  This can have a shocking impact if the cables aren’t shielded like Nordost.  
More you share, the more we can help.  

Nothing there to smooth things out. Perhaps some variation in component style. More warmth.