I own an Ayre KXR Preamp. NO listening fatigue over here. My whole system is Tara Lab Golds IC's. Running Pass Lab Rushmore speaker / amps with new RAAL ribbon tweeters. The harsh highs you heard is not from the KXR pre. Noticed system cabling needs to come off the floor for a start, and maybe some room treatment.
Sammy, I never said the KX-R was harsh. It's super smooth/clean. It gets fatiguing because the highs seem tipped up (i.e. an imbalance in my system). I could perhaps get around this by re-positioning speakers, but didn't have the time to try that when I auditioned it. If I found a used one I might buy it to give me that time - it's a great preamp for sure.