The best replacement for hd600 is hd650.

The best alternatives to hd600 are rated as following:
★★★★★  hd650
★★★★  dt880
★★★★  hd598
★★★  hd800
★★  he 400
★★  he-500
★★  hd580
★  k702
★  k701
★  akg k702
★  q701
★  hd700
★  fidelio x1
  dt990
  sr325
  grado sr325
  hd595
  akg 701
  mad dog
  beyerdynamic dt880
  lcd 2
  hd 650

Your alternative for hd600 is not listed? Suggest!
Speaking about hd600, one probably shouldn't forget about fiio e17.

Other search terms related to hd600 and their ratings are:
★★★★★ fiio e17
You have in mind a companion for hd600 and it is not yet here? Propose!



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hd600
hd650
dt880