This might or might not be relevant to your case but I’ll throw it out there anyway.
I went through a tonne of research trying to understand impedance matching with gear and headphones, and trying to work out technical specs of headphones and just generally how to get the best sound quality… Only to find that the headphones weren’t the weak point!
I eventually found that for a lot of amps (not sure if it’s common across the board or just on cheaper combos) the headphone circuit seems to be separate and actually skips some of the amps shaping so it sounds completely different.
You can get some combos such as the Orange Crush which has a cabsim feature that emulates the full amp speaker tone through headphones.
However I did buy a couple nice Sennheisers during this process because I needed to upgrade my general listening cans anyway, and I learned some things so it wasn’t a complete waste of time 