headphones gives you a wrong picture of the music. it's not related to how good the headphones are, it's related to the fact of them being headphones. because you use headphones, it's much easier to notice individual sounds and it's very easy for the brain to seprate stuff you hear, so it sounds killer on headphones and then when you get to real speakers it's all wrong. it's very hard to notice level differences in headphones. bad for the mix!
that's not all. good acoustics are very important to get the "feel" of your track. eliminating acoustics completely is bad.
in short, don't mix with headphones. don't write music with headphones at all actually.
sony sucks because a. they're not comfortable b. they break easily. and you get get better stuff like sennheiser or AT or beyerdynamic.