😄
This spring I tested the DT770-Pro 80 Ohms followed by the HD560S. Both were plugged directly into my PreSonus Studio audio interface.
So with the 770s I noticed I had to crank up the headphone output quite high to get proper volume (with the VST digital signal at 0dB). That had me worried about the 560S for, indeed, their ~120 Ohms impedance.
But lo and behold: when I hooked up the 560S, to my surprise I had to lower the headphone dial on the audio interface a bit instead of going further up as I feared (there wasn't much leeway left).
So what I (think I) learned is a difference in efficiency: higher impedance but more efficient == good or even better volume anyway. I'm not an expert but this is what I assume was happening.
When connected to my phone (which I seldomly do but for instance with the recent Modern D videos on YouTube), I have to almost max out the volume to get reasonable listening. But then, these are not phone- or consumer gadget headphones.
Hope this gives an idea,
Cheers,
HZ