Atmo- I read your comments about a tweeter's Unbearable Harshness of SS and hope you are somehow unaware of a cure. Cables?
@chorus I suspect you have a typo here.
The brightness is caused by distortion and because its in the amp, probably not something you can get rid of with an equalizer. It might be possible to use a ZOBEL network on the speaker itself, targeting the band of brightness, but since its caused by distortion the band is a bit of a moving target depending on the music and how loud its being played.
IMO you're best off going with an amplifier that doesn't exhibit brightness to start with! In the solid state world, that's a really tall order; a really short list. Since your speakers are easy to drive if I had to go with solid state I would be looking at an amplifier that runs no feedback such as Ayre or First Watt. If not available or rejected for some reason, a zero feedback class D amp is worth looking at too.