Just upgraded my ATH m50s to the HE-400 and I'm loving it so far.
I'm not currently driving the headphones through anything but my Asus Xonar STX soundcard with the factory default opamp. Would getting a dedicated amp do a huge improvement to sound quality? Would buying a separate opamp to replace the factory default JRC2114 opamp do much?
From what I've heard regarding opamps rolling, changes are very subtle. A dedicated amp would probably give more desirable results, but keep in mind the HE-400 is not hard to drive at all.