Preferred over 6xx
TLDR; These produce the sound I've been chasing by EQing my 6xx. Get the 2.5mm balanced cord with these if you have a balanced dac, you won't regret it. My new favorite, right next to the hd600.
As much as I appreciate the clarity of the 6xx, I always found myself placing a wide cut around 4-6khz and boosting the bass and sub bass around 30-60hz. The 58x produce the sound I was seeking right out of the box, at half the impedance at that. Also, I truly believe the 2.5mm balanced cord noticably improves these headphones in clarity as well as sub-bass, whereas I think it hurts the sound of the 6xx overall, which is unfortunate since the 6xx could really use the extra power provided with a balanced connection.
I've always been one to tweak the EQ to my preference per artist, but I love the sound of these flat for practically everything. Mid-range is silky smooth as always. Much more enjoyable for long listening sessions at higher volumes. The tighter bass and smoother highs is worth the small loss in clarity to me personally when in comes to enjoying music. I'll be using my 6xx exclusively for gaming now.
As a side note, the imaging is the same as the 6xx, so if you're looking for a wide soundstage, you may want to look at the he4xx.
Would recommend to a friend.