One thing I noticed is the different Ohm options for the DT770, what do they mean?
It tells their AC resistance and do they take power as voltage or current.
All versions should have basically identical power need (same efficiency in making sound from electric power) but higher ohm versions need more voltage while drawing little current.
Power = voltage * current.
Or P=UI in easier to handle form which can be related to I=U/R of Ohm's law
In device operating with very low voltage headphones simply have to content with low voltage.
But in general situation has gone totally nuts in chasing low ohms and more volume.
(higher volume sounds better even if actual audio quality decreases)
Despite of general public hallucination lower ohms aren't actually easier load for outputs.
It's current which causes stress for outputs and unless headphones need higher signal voltage (for wanted volume) than output can provide higher impedance headphones are actually easier load.
Higher headphone impedance also automatically improves electric damping factor with voltage source of output (and signal) having tighter control over movement of driver.
Not to mention less frequency response changes from output impedance (or serial resistor volume adjusting knob) if impedance isn't same at all frequencies...
Many popular Sennheisers are big offenders in uneven impedance and IEMs can have crazy impedance curves.
Because of average efficiency in general Beyerdynamics aren't that demanding load.
Basic integrateds of motherboards can drive 250 ohm DT990 well past hearing safe (for longer duration) volumes unless audio signal has very high dynamic range with mostly low level signal.
Was actually positively surprised when trying that after getting my DT990s and expecting inadequate volume and low sound quality/interference.
While having lowish ohms some AKGs are actually more demanding load because of needing more power, which at lower ohms means lot higher current.
Of course 600 ohm Beyers are again quite demanding for having enough output voltage reserve for all situations.
(though they draw barely any current)