Thx for sharing Peter. I'd like to offer a contrasting impression.
I had a decent amount of time with the XCs earlier before shipping them off to Currawong who has them now. At least to my ears they're still very much apples to oranges. Having them side-by-side driven by the ALO Studio Six & a modified Eddie Current Zana Deux (with a mod 3 ohm/12 ohm switch like the newer SE sibling), I found myself picking up the TH-900s more for enjoyment. I'd probably agree the XCs sound natural although for some reason still not "neutral" but can't put my finger on it.
In the end, the XCs sounded too closed sounding for me and would pick up the TH-900s over it at every listening session. The experience was the same for my wife - although not an audiophile she has more sensitive hearing for me. I also shared my experience with Bootsy1 but that was driving the XCs from a portable deviec (HM-901, Tera/Vorzuge combo).
So it's very much personal tastes IMHO. I'm somewhat surprised that the XCs have managed to "convert" two TH-900 owners but glad they have found something more suited to their liking. For myself, I think I were seeking for a contrasting sound to compliment my TH-900s, there's a high chance it'll be the Alpha Dogs instead of the XCs.