Interesting post. I hear something like this too on a variety of music. It's an upper midrange/lower treble harshness that sounds like distortion to me. I have wondered if it is something in my hearing because it can be worse or better depending on the day. I just turned 71 so I'm always afraid that maybe the problem is with me.
I'm using Thiel CS6 speakers and Krell amplification. I just bought a pair of Dynaudio Confidence 60's but I haven't put them in the system yet. I'm interested to see if they have the same effect. I didn't notice this when I was auditioning new speakers.
I have run REW and my decay time is around 550 ms which isn't too bad but I'm going to work on bringing that down to around 350 to 400. The waterfall plot is quite good so I don't think there are any room interactions that is creating this problem but I am on a quest to see if I can tame it.

