I have had my HD650's for a while now (about 3 months or more) and they sound great coming straight out of my motherboard which is advertised with a 600 ohm amp; here is my motherboard: http://www.amazon.com/gp/product/B00K23BYCI/ref=oh_aui_detailpage_o01_s02?ie=UTF8&psc=1 I just got the Phillips Fidelio X2's a couple days ago and I think they sound pretty similar but have brighter highs, more sub bass, better bass overall, and a better sound stage. I think the mids on the HD650's sound better though and I like the size and fit of them much more. I wish I could have the HD650's with the Fidelio X2 sound. My question is, can I get more sub bass so I can feel the rumble and like the X2's give by pairing my HD650's with an amp (either SS or Tube) and dac? If so I would definitely keep the HD650's because that's the only thing that I really feel is missing from them. The sound stage although not as good as the X2's as I have said is good enough for me and my genres. Also the highs don't matter too much because I don't see much of a difference between them and I like a darker headphone anyway.