What is wrong with my system?

Work with what you have before exploring equipment changes. Check speaker connections to make sure that the speakers are in phase. Try different speaker positions... closer to the wall for more bass.

I’m not a fan of b and w but they are competent in design and manufacturing.  Classe amps are more than adequate to deliver drive any speaker even with a demanding resistance and phase angle. A Bryston preamp is a neutral device that will drive any amp without coloring the sound, and certainly would not suppress the bass.
I agree with placing the speakers closer to the back wall for reinforcement.  My suggestion is front end.  Perhaps a denefrips aeras or audio gd r1 and use downloaded files via usb or a streaming service.  These r to r dacs have an organic quality that many find closer to analog sources.  To quote mr Atkinson. The future of audio is digital, it just won’t be spinning disks 

Many great suggestions here. I agree with trying 'no cost' or the cheapest changes first like room placement, etc. As for cables (which could be the issue), check out the Cable Company (www.thecableco.com). They have a lending library where you can audition cables then return the ones you don't want. That's a good way to experiment with other cable brands. And definitely check cable placement--I accidentally crossed speaker cables once and the sound was really weird. Once I double checked all the connections---voila! Everything was right again. Good luck and let us know what you end up doing. 

the importance of room placement.


I doubt room placement is going to fix this problem, it will help a little, but it’s still going to be bright and analytical. I had the same problem as the OP a few years ago, a krell amp and a solid state preamp it wasn’t even listenable. I have a dedicated room and placement didn’t help much. I inserted a tube preamp in the chain and it’s very musical now, I actually think I’ve gained some detail without that bright sound etching at the ears.

I hate to burst your bubble but any B&W that I have listened to are bright. Any change that you decide to make you will still have the problem till the cows come home!