I'm on the market in search of a pair of good headphones. My price range would be around $150-$200. I like to listen to orchestral (soundtracks), rock, dance, kpop, trance, and some metal. My main thing would be soundtracks. I've been looking through some Sennheisers and Grados but I can't really make up my mind, since I don't know much about headphones. And when I do buy it, would I need an amp? I don't understand what a DAC is, and all I know is that amps bring up the volume and make the music better? haha I have no idea T____T" I currently use my iPhone 4 as my mp3 device.