[Parall3l]

I'm not an engineer so I can't explain what makes an amp good or bad with scientific terms. Theres some obvious things you can hear with your ears though. Like hissing or distortion.

 

[Craigerson]

i'm a little new myself so i can understand where you're coming from.

any cans that are recommended, in my opinion, are good. i went for a pair of ATH-M50s a couple months earlier and was very happy with them. just choose the ones you like, not what people tell you what to like. read the reviews thoroughly and make an educated decision. your taste is entirely different from everyone elses.
 
as for the amps, they do make a difference in your headphones but it's not like an out of this world experience. at first, i was expecting them to be like.... LOL OH MY GOD, SO THIS IS MUSIC due to the dumb praise given to my amps. instead, they're like a 20% difference in the head phone. which does make it noticeable but not necessary for entry level headphones.
 
spend your money on a headphone first and foremost. nothing is more important than the headphone itself. no headphone, no music.