Previously the 1266 TC wasn't always my favorite headphone. There's one aspect which all this while bugs me, and that is the tonality and timbre. I always felt it's a bit off, treble sounds unnatural/metallic and bass sometimes becomes overwhelming. After using Mitch neutral-bass filter, it has somewhat improved but I still prefer my other headphones. It came to a point where I put my TC on sale but somehow nobody wanted to buy them in my country. However, for this past one month or so, I've been listening to it more frequently out of my 300B preamp + Primavera combo (+ still using Mitch neutral-bass filter), and voila, I no longer have this timbre issue. Everything sounds so natural, very even frequency from top to bottom, a very full, seductive and forward midrange, and treble is much more natural than ever. Although soundstage is not as wide or open as from my CFA3, but still has very very good depth and layering.
I'm glad it works out and I don't think I will put the TC on sale in the future. Very very enjoyable with my music genre (jazz + classical).