Speakers sound too bright.

I would think it's primarily between your ear and the speakers. If they sound too bright, your ears are telling you what you may not want to hear, no pun intended. I would not tweak anything, but return the speakers. 

Or you can buy and EQ, quickest and cheapest trick.

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.