KeLLzDepends on your budget, from what I've heard and owned from best to worst(worst with these headphones still sounds perfectly fine) in my personal preference with the HD6xx it's like: Woo Audio WA2 > Schiit Mjolnir 2 > Jotunheim = Audio GD NFB 11.28 > Magni 3 > portable amps in the price range of $80-120 = decent PCI sound card > internal sound card = ipod/phone
E111I have a sound blaster Z and I think this is accurate. My home theater receiver sounds noticeably better than the Z, which sounds noticeably better than my phone or Chromebook. On the phone or chromebook, they sound pretty bad on the low end.