So I finally bestired myself to convert the Silver Dragon cable for my HD 800 to a HE1000 cable. In short: It brought all the smoothness and sparkle I was looking for – along with further membrane break-in and more sophisticated equalization. Now the HE1000 sounds absolutely convincing to me in every respect: bass, midrange, treble, extension, clarity, transparency, soundstage, detail, dynamics/impulsivity, neutrality and particularly naturalness. From the headphones I've heard it's the one with the best, most careful reproduction of instrument timbres.
For those interested and in possession of a FiiO player or any other octave equalizer, here's my latest EQ curve (from 31 Hz to 16 kHz):
–– –– –– –0.2 –0.2 –0.2 +1.6 +3.2 –1.8 +3.6
Although certainly many HE1000 owners would call themselves perfectionists, I'm possibly the only one caring for an optimized frequency response (roughly on the basis of Tyll's measurements). Whereas most seem to content themselves with the «factory settings» of their gear.
If you're trying these settings, give yourself some time for adaptating to the new sonic balance! And after that you may feel the need to adjust it to your liking (or your individual HRTF, resp.).
I have been given some advice to use a beefy/TOTL amp for driving the HE1000. What I can say is that the quality of the amp will certainly be reflected by the headphone's high resolution. But at the same time if your DAC can drive it directly, with low enough output impedance and high enough output power, any amp in the signal path – as good as it may be – will audibly degrade the signal.* I tried to use my Chord Hugo as a mere DAC, feeding three of my amps. The EAR++ III (Black-Gates modded) sounded very pleasing at first, mighty and smooth, but after a few seconds it became too clear that it makes the sound slow, thick, round and intransparent – almost a caricature of euphony compared to the Hugo driving the HE1000 directly. The Corda Concerto was better in terms of accuracy, but failed to create a natural sound, still made transients slower and sacrificed clarity. The best of my amps was the Corda Symphony: Although transparency was reduced and transients were rounded, it sounded passably neutral and detailed. But still far from the Hugo's headphone out, which was a class of its own, in every tonal aspect – dynamics and bass punch included.
This just as a hint for those who try to equalize the HE1000's tonal traits by means of synergetic electronics. For me the Hugo/HE1000 pairing (plus a matching EQ curve) provides a sound as close to my sonic ideal as it gets (from what I know and have auditioned).
* The kind of signal degradation introduced by amplifiers doesn't necessarily sound bad; according to my experience it will make the sound more forgiving in view of the headphone's inaccuracies, particularly frequency-response issues and resonances. Even harmonic distortion can be masked by the smoothing effect of amplifier sound. And primarily the sound may become bigger and fuller.