Isn’t it that if it’s brand new gear it needs to be broken in a little to smooth out some of the edginess.
New cables can offer a bright sound and then when used for a while they soften.
During the waiting period and if you have tone controls you can reduce the treble. And then bring it back after the warm up phase.
Also a lot has to do with ears adjusting to the new experience.
You may notice brightness but you also may want to consider the improved detail elsewhere as a way to appreciate improvement of system