I've had the B&O H6 for around 2 months now, using them daily during my commute, a replacement for my DT1350.....and I have to say, they are absolutely, stonking brilliant!
I picked them up for a great price on these forums, in mint condition, and while I originally had reservations about the bass, I now hear what "quality" and "layered" bass is all about.
Here is my comparison to my 5+ year old Beyer DT1350, which were previously used on my daily commute Both driven by the iBasso DX50:
Mid Range
DT1350: Forward, clear, at times "shouty" but nonetheless very enjoyable and a focal point of the sound signature (along with bass).
B&O H6: Well balanced, forward but not shouty as the DT1350. Generally very smooth and very pleasing. Its clear and upfront in the soundstage.
Treble
DT1350: Detailed, clear, not piercing at all.
B&O H6: Same as DT1350.
Bass
DT1350: Hits very hard, good slam, lots of mid bass.
B&O H6: Also hits hard, not as much mid bass as DT1350 but better sub (low) bass. Has much better quality bass, the layering is noticeably better. The bass really took me by surprise on the H6.Very enjoyable.
Soundstage
DT1350: Closed, narrow, in your head sound, congested, the low point of the sound signature.
B&O H6: Brilliant, open, clear, out of head sound with certain tracks, the soundstage helps create clarity with instruments, increases perceived detail retrieval.
Comfort
DT1350: I've worn these for 6 hours straight. Yes, it hurts the ears.
B&O H6: Just lovely, light as a feather, lighter than DT1350, no comfort issues at all.
In conclusion, these are my favourite headphones I currently own. I've owned many headphones over the years, some mid range, some high end. The H6 are one of the cheaper headphones I have purchased and I actually consider these the overall best I have ever purchased. The comfort, the sound, the closed back design, the aesthetics, removable cable, dual entry cable option, build quality; it just ticks all the boxes for me.
The Danish really know how to produce great sound. Thank you Bang & Olufsen for giving us a well balanced headphone, a jack of all trades if you will.