Depends on the sound card and the headhpones. A good SoundBlaster sounds just fine with 200+ ohm headphones. It's just that, well, use the search function:
Anything pushing 10mW or more with an output impedance of less than 4 ohms will drive K55x just fine.
I don't need to search anything. I've never heard an 'upgraded' soundcard alone sound better than a dedicated amp or amp/DAC (portable or desktop). But hey, that's me. I prefer better amps not just for the power, but soundstage, clarity and as black a background as I can achieve (and I don't listen at loud volumes). To me being able to drive a headphone doesn't mean it will sound good.
Edited by x RELIC x - 6/20/14 at 10:16am