https://www.amazon.co.uk/gp/product/B00Y2EOI94/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
My fave cans atm. I've got them on a two stage set up. I'm using a Little Dot MKII for the pre amp (four valves) and a Graham Slee Novo for the amplification because the ohm load for them did not sit well with the MKII (being all valve based it lacks power).
Absolutely the best set of cans I've yet used for bass heavy music. They're planar magnetic, which I would swear makes a difference to how the bass drops. Normally if I wanted lots of bass on another set of cans I get this issue where when the bass hits the volume drops.
Any way, I initially had them with a Little Dot MK1 (valve + trans) and for the money (about £320) it was the best set up I have ever heard.
I still have my Grado RS2E and B&O H6 up on the desk too. I use the Hifiman for anything beat/bass driven (I'm a sucker for an SPL bass test CD

) my Grado for anything live and the H6 for gaming and listening to when my lady is in the room (the others are all open back).
But yeah, Beyer ETC are not what I would call elite tier really. They make some nice cans, but Hifiman are pure headfi. The He400S are a plastic version of a far more expensive set of cans and it shows IMO.
I also believe that (so far) I have not heard one set of headphones that can perfectly nail every kind of music. My Grados are the best set of cans I have ever heard for live recordings and some rock music, but lack any sort of rumble or thump that you need for bass driven music IMO. The B&O H6 are somewhere in the middle, ideal for fast BPM driven music and fast paced techno and the Hifiman are for when I want the bass to really drop

but their clarity whilst they do that is something I have never experienced before.
I shall have a look although a friend of mine just messaged me on Facebook asking if I'd want to buy his Phillips Fidelio X1's for £150 which have been worn for less than a day.
I'll have to do some research on both the Sennheiser 598's and the X1's
Unless you listen to a lot of classical music I would be quite careful with the Fidelos. They're very much akin to Grado and whilst they are unmatched at that sort of music I have duly noted that you usually have large cans.
If you want the best hifi experience of your life? get the Fidelos. If they are even half as good as my RS2E then they will be an experience. The soundstage on my Grados is just haunting. However, they're not a jack of all trades and thus when I want to listen to something a bit more chav (born and raised in Brixton, take the boy out etc) or bass driven they don't cut the mustard at all.
Give the Hifiman a go dude. Pair them up with a Little Dot MK1 and you'll have a right laugh.