One more idea: your hearing might be exceptionally good. The PSB Synchrony models have an unusually low spike at the tweeter's resonant frequency, around 16-18 kHz (or maybe this is simply a spike in the treble apart from the resonant frequency). It's possible that (like me) you're still young enough that your hearing extends up this high and you're bothered by the spike, finding the sound fatiguing. From JA's review of the Synchrony One:
"The top octaves sounded smooth to me on this Telarc SACD—the delicately brushed triangle at the end of the final variation before the fugue was beautifully resolved, without sounding spotlit—but Erick Lichte was less tolerant than I of the PSB's performance in this region. However, in the "Measurements" sidebar accompanying this review, I wonder if he was reacting instead to the small response peak between 16 and 18kHz, which, unlike me, he could hear."
http://www.stereophile.com/content/psb-synchrony-one-loudspeaker-measurements
This could create listening fatigue for you and possibly (my dead horse takes a further beating) trigger the acoustic reflex--further creating a perceived tipped-up tonal balance.
"The top octaves sounded smooth to me on this Telarc SACD—the delicately brushed triangle at the end of the final variation before the fugue was beautifully resolved, without sounding spotlit—but Erick Lichte was less tolerant than I of the PSB's performance in this region. However, in the "Measurements" sidebar accompanying this review, I wonder if he was reacting instead to the small response peak between 16 and 18kHz, which, unlike me, he could hear."
http://www.stereophile.com/content/psb-synchrony-one-loudspeaker-measurements
This could create listening fatigue for you and possibly (my dead horse takes a further beating) trigger the acoustic reflex--further creating a perceived tipped-up tonal balance.