Well, you're certainly right about no recorded music being accurate. Yes, it's just not. My point if contention was, and still is, that even-order harmonics have been wiped from all recordings unless tube gear has been used in the process. Because, for one, there is a DAC with the above mentioned THD, the Chord DAVE, with very little ,to no, negative feedback. Therefore, if it cannot be measured, or heard, the negligible distortion that we are talking about simply cannot be a product of the absence or precense of tube gear in the recording process; it's simply the recording process, itself, that is the culprit of inaccurate sound reproduction. After all, from roughly the 1920s to the early 1980s all music was recorded with tube gear, and even to some ill effects, like let's say the tube compression of mid-60s Kinks and Beatles.
That said, I HAVE read the papers and studies of tube amps, preamp, monoblocks and buffers have a more soothing effect on most listeners, as opposed to solid state. This seems to be a given. Has iFi found the golden balance, though, in such a little object? I know that my couple of years with the iDSD micro would hint to yes. Tubes through cans, though? For these ears the effect has never grabbed me, probably because headphone listening is very much an in-the-head experience, and any nuance distorts the product is felt too intimately - like tubes. I might be in the minority there, yet I'm also very sensitive to ear fatigue with dynamically compromised audio with cans.
Anyway, so that we're not dancing, I have little doubt that the iTube2 is a fantastic product. IFi gears plays extremely well with other iFi gear, so the synergy therein is probably amazing. It's a bit strange, however, that I've found that iFi stuff doesn't always mate well with other manufacturers, which is why I'm hesitant to see if it shakes hands well with my DAVE.
(If there are any typos, forgive me, because I've been typing all of this from my phone.)