Hello, thanks for answering. I will use an ipod classic 160gb, just because it's the only one that can get all my music, and yes, I will also look for an amplifier. About music format, it's mainly alac, converted from flac, or 320 mp3, but of course some albums are in bad quality mp3, as it's impossible to find better quality ones... I don't understand the "sound signature" meaning, could you explain me that? Thanks again, awaiting for answers!
He's asking how do you prefer your headphones to sound. Since you listen to a range of things, you may not entirely be sure. That's fine. Nothing like trying out a lot of different cans to figure out what your preferences are. That's what I did (and continue to do). If you're really trying to get portable, there are some great, highly efficient, over-ear cans out there that don't require any amp at all to sound good. Start with the Logitech UE 6000, V-Moda M100, Sony MDR-1R, and Sennheiser Momentum. The Momentum is slightly out of your price range, but you should just hear it because it may make you want to up your budget that slight amount.