[jadawgis732]

I currently own only one pair of full-size (ATH-M50) and 3 pair of BA-IEMs (Klipsch Custom 3, Ety HF3, and Brainwavz B2), and listen to all sorts of music - but primarily classical and rap (yeah, not a typo).
 
I'd like to get another pair of full-size, either a pair of either Sennheiser HD600 or HiFiMan HE-400s but my sole source is an iPhone 4s. From what i understand, you just don't pair 300Ohm headphones with an iPhone because it'll drain the battery very quickly. I'd also like to use these on the bus, walking around campus, etc. I also understand that electrostatic headphone don't usually have high impedance. So I was thinking along the lines of the HE-400. Could an iPhone drive them well?
 
What would be your recommendation, and why? Any and all help is appreciated.
 

 

[flatmap]

I find that open headphones are pretty frustrating for portable use.
Too much of the outside noise leaks in. 
 
I can, in a limited sense, run my HD 650s from my iPhone.  They get as loud as I want.
There's enough bass, but not the same subtlety, clarity and zing that you'd
get through an amp.  So you don't get the full value, unless amped, in my experience.
 
Of course one way to think of it -- get the headphones you want now, use them,
and them save up for an amp later on.  Not sure what the HE 400 would be like,
but hopefully someone else can chime in.