I recently tried the Formula S+Powerman combo, Enleum Amp-23r, Luxman p-750u, and Ferrum Oor+Hypsos with my Diana TCs and the one that really brought them to life was the Ferrum combo. Some nice things going on with XI Audio and Enleum, but with the Ferrum setup there is so much speed and bass power and the tonal balance is almost faultless.
I think those who have been dogging the DTC have not been using the right amp, because right now this setup absolutely rocks. I was going to post an in depth comparison between the LCD-5 I have for a few weeks and the Diana TC, but I've made so many source changes. I ended up returning my LCD-5 feeling pretty pissed that they had deliberately tuned it to sound bad, obnoxious upper midrange and thin bass, and used the refund money for the DTC.
To summarize, at least on low-medium power amps, the Audeze had a more balanced midrange except that ghastly 3.5khz hump, and more speed and dynamics in the midrange. But the DTC was more comfortable, musical, much better bass (power) and treble, deep black background and rich tonal colors (unlike LCD-5s greyish sound), better spacial contrast (compared to Audeze more etched edge-contrast), and overall sounded less clinical and more vibrant. Once I got into some more powerful amps like the XI Audio and Ferrum, the less balanced "W" shape of the midrange seemed to disappear into a more linear and full sound. At this point I am very happy with the Diana TCs.
Maybe a better amp would have fixed the LCD-5? But it was painful to wear, clinical, and I just can't forgive them more now unpleasantly tuned it is. Whatever the philosophy or thinking Audeze has where they take a line of amazingly tuned and musical headphones and then make their flagship and deliberately nasal and unpleasant sounding tuning with the idea that you use EQ to fix it, I'm just not on board with that at all. It's got to sound decent with extra DSP. Diana TC got it right, and I've never heard another headphone with these same vibrant colors, deep black, and subwoofer like bass (haven't heard the 1266).