The FiiO E12 does 'significantly' increase the sound performance of headphones; i simply can't listen to any headphone without an amp now, it's just not worth it, it's like going from a car to a motor-bike, the comfort and luxury is simply not as good.
Without an amp there is no power and drive to the sound, it lacks lustre, and sounds totally dismal, but plug in the amp and BANG! wow we're talking. Not just volume, but every sonic aspect and performance of the headphone significantly benefits from the amp. Once you go amp you never go back, it's as simple as that. I say get the FiiO E12 man, excellent value for money and very noticeable performance gains and quality, clean and balanced and powerful.
Agreed. If you are running your iPod or Macbook at higher volumes and/or using EQ to boost the bass, then a headphone amp could be a very good idea. It can give you cleaner output because of the extra headroom. At low volumes, you might not notice much difference.
E11 has especially good bass boost if you are looking for that. E12 is even better in overall amp quality. If bass boost is not important and you want a good amp, C&C BH is very good. It has a switch for expanding the soundstage (makes the sound seem to expand outward). A nice feature for the M50s since they don't have a very big soundstage.