I'm looking at these at the moment.
They'll be mostly use at home, most of the time i just fall asleep with my music.
are the metal part on the side solid? can i fall asleep with them without worriying about founding them destroyed next morning?
are they good for Rap and RnB?
How different the amp bring the sound compared to an ipod touch 4gen?
portable amp possible?
As long as you don't toss and turn a lot after falling asleep, they should be fine...they are quite solid and quality built. I think they are pretty spectacular for Rap/R&B/Soul personally. I would definitely advise that you get an amp. For a portable setup, I would have to recommend the Fiio E17 (though I've not personally tried it) - it seems to be a good pairing for most HE-400 owners. Plus, it's EQ and features are said to be very good. The best way to use it with an iPod is with a LOD (line out adapter http://www.fiio.com.cn//upFile/20125494653.jpg ). Otherwise, you could connect it to a laptop via USB. How portable would you like it to be?