OK, I listened to the XCs again a few hours later and they settled down a bit, but still forward. I then tried it straight into my AK240 and it actually sounded better. I may need to burn-in the headphone section of my Glow tube amp; I've only used it for speakers in my bedroom since I bought it new a year ago. I can't recall if the circuit is straight off the tap or independent. I still haven't tried my Luxman tube amp yet, but now I'm more hopeful.
When I first listened to the XCs earlier today, they reminded me of my experience with the AKG K701s which I bought when they were first released; I did not like these headphones at all even after 500 hours of burn-in time. Felt like an icepick stabbing my brain, figuratively speaking of course.
I live in the Santa Cruz mountains in northern CA, so I hike quite a bit. I took my new XCs with my 240 and went for a short hike—about 2.5 miles—just to see how they would work during this activity. The weight of the XCs didn't bother me at all and the clamping force kept the XCs snug on my noggin. If the upper mids warm some more, I may have my dream portable system.
Here's a couple pictures for you all ... my XCs and my fellow lambskin leathered, wood ESW-9As.
While I find the X and XCs sound great from portable players, they really sound their best on a good desktop amp IME.