brightness in my system

need to know the components in your system to properly diagnose the problem. are you using a preamp?

I have a 15k system with MIT cables and as the other post suggests, they will improve your system.An extremely low cost tweak would be to get a CD Blacklight mat.I have one and confirm that it will take smoothen the edge of off highs

First change your cables, especially loudspeaker cables. I recommend you MIT terminators. You will elliminate most of the brightness. Another thing is, if your source is digital, most probably you have a lot of jitter, go with Monarch DIP jitter filter(very cheap but fantastic) or go with Genesis Digital Lens (expensive but valued), you will be ending with majority of your brightness