This One has Me Stumped

I recently purchased a Pass XP-12 to replace my aging ML 38s. After installation, I noticed gobs of high frequency distortion, especially in Operatic female voices.

I measured every component in the signal chain separately. All are performing in spec.The XP-12 has very impressive test results.

Re-installing the 38s gets me immediately back to more mellow sound.

In my system, I have an EQ and crossover between the XP-12 and my Bryston 2.5b^3 power amp. I removed the EQ and the XO, plugging the XP-12 directly into the power amp. The distortion remains.

I am puzzled. I am a measurement guy. I use REW extensively. I can measure and troubleshoot almost any problem in my system. This one is a stumper.

Can anybody suggest a measurement or a way to solve this apparent component mismatch?

 

My system in order from source to output :

Shelter 901 MKIII MC or Koetsu RS MC cartridges

Parasound Zphono XRM phono preamp

Technics SL-1200G TT

Oppo BDP-105 Universal player (digital)

Bryston BDA-3 D/A ( feeds the Oppo signal to the XP-12 or 38s)

Sansui TU-X1 tuner

XP-12 (38s) line amp

dBx 1231 EQ

Rane AC22 2 way crossover

Bryston 2.5B^3 power amp

Usher 604 floorstanding speakers

HSU ULS-15 sub (when using the XO)

 

Thanks,

Kevin