Just to go back to the original topic, my new (made in China) K702s arrived today.
They sound similar, I think the lack of bumps on the headband have made them slightly less comfortable and they are easier to drive than I remember!
Using an Apple USB C to 3.5mm adaptor from my computer I only need the volume at around 11% for normal listening from Spotify (with volume normalisation turned off), this fits in line with powering them from my Panasonic receiver and I even get sufficient volume (no outside noise) when using the Apple USB C to 3.5mm adaptor from an Android phone, pretty sure the output is limited at either 0.5 or 0.05V from the android phone.
I'm going to say these are not a power hungry headphone, also from
@solderdude's website, because the impedance curve is fairly flat the frequency response shouldn't be different if the headphone amp has high or low output impedance.
One thing about the K702 is they really challenge my notion on whether burn in exists or not (I don't really believe in it but the K702s seem to change a fair bit), I remember burning my old made in Austria set in for like 300 hours and it being smoother afterwards (in line with a lot of other forum posts I've seen for these cans) and it seems the same thing is happening over a day of listening today.
The first song I listened to on the K702 today was 4AM by Grimes and it was very harsh (almost like whatever the song was mixed on had a dip in the FR right where the K702 has a peak) I've taken notes on how it sounded and I'll revisit this in a week or two