One last item: interpretation is everything! There was a guy on this forum a couple of months ago that had tried upgrading to a much more expensive DAC. He tried using it and switching with his earlier less expensive one, but every time he was getting grain and sibilance with the much more expensive DAC. His earlier one seemed to have a much smoother sound that he liked. He eventually returned the expensive DAC not understanding why so many other folks on the forums liked it.
The problem was that he had bad source equipment and recordings. His old DAC was smearing the treble details during playback of his source equipment and giving the illusion of "smoothness" where the newer more expensive DAC was accurately passing all of the micro details from the bad source through. Because the DAC now gave him more details (including sibilance from his source equipment) the SYSTEM sounded trashy and he blamed the DAC. So he went back to a system with no details but smooth sound.
The synergy in audio systems frequently precludes "1 piece upgrades" where each upgrade makes things a bit better. In many cases, adding a single higher grade component can make the system sound worst by destroying synergy that was in the original system.
It's maybe why I prefer the DT880 03 over the T1 on some track, but I feel it's the opposite, the DT880 show a bit more in the upper range then the T1 and it allow to ear the texture in the sibilance, the T1 doesn't seem to be as good.
But I can confirm that the dac make the difference, I want from a onboard sound card to a W4S Dac2, and it sound much much better, I think it's one of the best upgrade I have done so far. It's a bit less neutral then my SPL auditor, so it show a bit more bass and it sound more relaxed. Even my pc speaker sound better since they are connected to the dac.