okay. i must just not have seen the usb on the specs.
remember your soundcard already has an amp inside it powering your headphone drivers.
if you were talking about pushing out more power than the soundcard can handle by lets say using an external headphone amp then that would...
A)be very costly
B)may blow your drivers since they are not meant for big amps (headphone amps are meant for larger driver and typically higher ohm studio headphones and the like)
C)if they do not blow your drivers would not result in better sound
D)since you would be doubleamping (soundcard has an amp, combined with an external) you would have a higher %THD (distortion) which means it could potentially sound worse.
generally the only thing you would need a...