number1sixerfan
Headphoneus Supremus
Stax headphones all have exceptional upper mids (my favourite is the 007mk1 which, unusually for estat, also has a good bass)
Agree, based on the description and question, I'd definitely recommend stats (if feasible).
Sennheiser HE60 is the absolute reincarnation of the HD600, and a whole world better if you can find one. 009, CRBN or x9000 may be worth considering if not. 009 does a lot of what the Susvara does, just a bit more technically proficient in some areas and also more bright. I would probably start there if you can't find an HE60.
But then again, requires a new amp for most. So I know it may not be worth considering depending on your current system.