Speakers sound too bright.

I purchased a pair of Zu Soul Supremes and had the same issue. I waited for break in and went past the return date. I never got over the fatigue and ended up selling them. Was able to listen to Audio Note e/lx and problem solved. I don’t blame Zu, since I know they make a good product. I think I have sensitive ears is all. Don’t make the same mistake I did and hope they work out. Try to break in and if they don’t get significantly better, return. No shame. 

You need to treat your room. Absorbers for high frequency 

preferrably behind them.  Will help a ton

good luck

One possibility. If these new speakers are 2-3db higher in sensitivity you may be playing them louder than the Kefs not realizing you need to lower the volume. Louder than normal levels can make mids and vocals a bit sharp or harsh.

Happened to me once. Upgraded speakers. Was testing them out on familiar music, but not remembering that I should have reduced the volume about 35% due to 3db increase in sensitivity. Once I realized this and lowered the volume I was very pleased with the sound which had sounded occasionally bright or sharp when I had the volume too high. 

I felt the same with the Klipsch RP 600M.  Sold them to someone else.

Following the thread I understand you have no carpet no furnishings nothing to dampen the brightness of the speakers. The room is as important as the system.

If you put furnishings in the room it's going to affect the sound just as putting carpet on the floor or putting up damping material on the wall. Not very many systems are going to sound good in a bare room. Speakers also need to be broken in as stated by other people on the forum.