Hi OneHorse. I have a very similar system. Focal Scala Utopia Evo powered by two bi-wired BHK 250 amps, BHK preamp, Venus 15 DAC, Aurender N150, and a Shunyta power conditioner / venom cables. When I first got these speakers I had similar issued with the high frequencies . I am a bit suprised that with your BHK gear you are having this issue. The Focals are very reavaling and accurate so I found that the electronics and room are going to be front and center. These speaker are not going hide the characteristics of your system, but if you feed them well, you will be rewarded. Message me if you want to chat. You have some good advice above - here are my further comments (right or wrong).
1. Your B&W may have been getting old so they had less top end. I find old speakers' sound soft - they lose crispness in bass and treble. I have listened to B&W and don't find them warm. This may explain the difference in sound as well as newer tech in the Focals adding a bit more/different. Your prior speakers were designed in 2005 and the Focals in 2017.
2. Treat your room - this is good advice regardless of what speaker you buy, and it was one of the biggest steps forward for taming my high freq. energy and improving quality. I want to stress how much room treatment helped. Treating my high-frequency reflections made a big difference. When you describe your room, you mentioned concrete. Your speakers generate amazing high-frequency detail, but the reflections can add up. Your top-line amazing speakers need to be put in proper room. I wish I would have started with room treatment. Was the demo room treated?
3. I started with a Benchmark DAC and the delta sigma chip was not a good match. Highly accurate, but sounded digital. It would have been a better match with a softer sounding speaker. I replaced the Benchmarks with an R2R Dac and run in NOS mode.
4. How are your tubes? I tube rolled my into a tube with a more relaxed sound (NOS on the channel that feeds the mid and tweeter) and new Rays Reserve in the preamp. I did not know the history of the tubes and some were basic entry level tubes. That warmed up the sound but I did not lose detail and got better sound stage.
5. If your speaker are new, yes, break them in. My speakers were already broken in so I can't comment on the break in change.
6. What music are you listening to?
7. What exactly don't you like about the sound? Sorry if I missed it.
7. If you can't undo the sale, give it time. Eventually, you may not like the sound - everyone hears different, and some people always want a warmer, softer sound. Nothing wrong with that. It's your system - make yourself happy.
8. I also did power conditioning and that helped with quality, but not sure if that would help your situation. Depends on the quality of your power.
Please let me know if you have questions. Happy to help.