Thanks, I dont really know much about headphones and I looked at tests and "distortion" confused me. I heard that DT are "sharper" than HD600, but maybe to sharp, so almost no one enjoys beyerdynamic because listening might be painful for them. Does the DT 990 actually have a wider soundstage than HD600?(My questions may be stupid btw))))
A little EQ for both models goes a long way.
With digital audio EQ comes for free.
When you EQ both to the same target it all comes down to price, comfort and looks up to somewhat loud levels.
When you want to go impressively loud distortion becomes an issue. This is what the plots show (how they react at high levels). Stay under those levels, so all-day listening levels where you do not get the urge to turn the volume down and when you hear a favorite song you turn the volume up.
The dip in the upper mids and treble peak can create the idea that the soundstage is wider. The treble peak gives the impression of being highly detailed.
While there is a treble peak the treble quality is very good so it does sound sharp but not coarse nor grainy. Just sharp.
The added warmth helps with bass-shy recordings.
Those that care more for 'clarity' and don't need 'Harman bass' (DT990 also is not Harman bass) and dislike sharpness will prefer the HD6*0.
So in short: when using EQ both are excellent and not too expensive headphones with a quality build quality and excellent support (parts)
When not using EQ these headphones differ so much that it is clearly audible for everyone and personal taste will be the deciding factor.
There is no right or wrong in a personal preference choice. When looking at things like 'neutrality' (meaning which headphone sounds truest to what's on the recording or mixing) the HD600 is the better bet.
The choice between DT900ProX and HD600 may be a tougher one and these are in a similar price class.