bigpeyHi;
I have HD 595 and just received this 6XX, which is barely better. More bass for sure, but i am not sure it's delivered in a way that makes me happier. Maybe my setup is no good, not sure. It's Spotify 320 - HP Elitebook - Jotunheim - HD 6XX, running unbalanced, still looking for a decent cable. You will need an Amp for HD 6XX for sure, its 300 Ohm vs 50 Ohm of HD 598
See here for difference between 595 and 598
https://homestudiobasics.com/sennheiser-hd-595-vs-598-the-difference/