Fair enough you do make a good point, I just don't agree with you lol. By OPs description of the sound I would prefer it too and that convinces me that they are functioning very well.

I know they are 120 ohms and not 300 ohms like HD600/650 but I would not consider 120 to be a low ohms headphone. More generally, it is an explanation for why they sound better out of OPs moderately high output impedance headphone jack.

HD560 and high-end Sennheiser headphones in general are high ohm headphones, built in / designed for a time when people still used their stereo headphone jacks which use resistors as you describe

The only problem with those headphones is a small tonal imperfection, which is 90% fixed by equalization. If you use a phone just download the Wavelet app and it will do it for you.

I agree with both of you and think that it shows that amps really don't matter because that amp is not neutral. There's nothing wrong with that, I also buy tube amps precisely because with the right tubes they are gooey and do not sound neutral either.

The '80s were such a great time. People were still optimistic, bands wrote their own songs, venereal diseases weren't fatal, people socialized face to face and conspiracy theory loving clowns were confined to basements, not the white house and supreme Court.