Im one of the crazy guy that bought both HD58x and HD6xx...
Bought the HD58x first but due to fomo, I implusively bought the HD6xx during sale.
First impressions, HD6xx has lesser bass than the HD58x, but not by a longshot, bass is still present but not as booming as HD58x, and vocals are way more pronounced. HD58x was more "exciting" due to more bass but vocals more recessed.
Definitely a vocal god-tier headphones, with that sennheiser "magic" sound.
This is not less to say that HD58x is missing the "magic vocals". With EQ, it is possible to bring out the vocals to similar quality of HD6xx.
I also owned the DT1990pro... quick comparison without EQ; soundstage, instrumental seperation on DT1990pro is more apparent & wider. However, the treble piercing vocals made it "difficult" to enjoy vocals. HD6xx was way more fun & enjoyable to listen to.
Source used: Apple music, Fiio e10k usb dac
Tldr: If your're looking for just 1 pair of all-rounder headphone and love vocals buy this.
Beautiful LOTR Board. A little clangy, like a metal clang that's a little unpleasant when typing but I feel O rings or maybe extra lubing would help. 10/10 love this board.
Matt3o did an amazing job and I loved how they came out. The profile ended up not being for me but didn't regret trying it out and would recommend if someone wants to try it.
I love these and really wish I could have gotten a second pair for when these eventually die. I haven't found another pair of headphones that is this comfortable and great sounding.