Speakers sound too bright.

Brightness (lack of) is not usually what improves with speaker break in. What you normally hear in brand new speakers is a "tightness", the speakers don’t swing and let go of the notes. And the bass can seem somewhat lacking, the bass and midbass fill in when the driver suspension loosens up.

That said, a speaker can sound top heavy if the bass isn’t balanced with everything else. A tweeter will sound more prominent in a bass shy speaker. That could be what you are hearing and that just might change with more hours.

How long can you keep the speakers and still exercise the return option? If you have time, put a track on repeat while you are at work and let ’em rip for a few days. If they haven’t come around after ~200 hours, send ’em back.

For everyone pointing at the room, I tend to agree that is a weak link. But the OP has stated that the KEFs didn't exhibit this behavior, so the room and the equipment are the constants in this scenario. Room treatment will certainly help any speaker perform it's best, but that might be the primary issue here.

Don’t get me wrong though, these 60xti speakers sound really good, just bad recordings sound bad and good sounding recordings give me goose bumps.
 

So what’s the problem? Do you want a speaker that makes bad recordings sound good? What you will have then is a very low resolution transducer. Think Advent speakers from the 80s. Pleasant to listen to, even with bad recordings. But very mediocre speakers.