I want it to be portable because I don't want it to a fixed placement in my house. I want to be able to move it from my computer to my x-box to my guitar rig(for the evening) and all around the house without moving a big headphone amp. Plus, being portable it allows me much versatility, which is a HUGE plus to me. For instance, if I'm at my GF's house and she decides to crack down on some homework and I can whip this out and relax. Portability is a huge, huge, huge plus for me. I'm not stationary that often (not like I'm out jogging or exercising with this rig, lol) But I do take it on the occasional relaxing walk, or to the park and such and sit around and relax.
I know, I know I should get something like IEM's for that, but I just can't take it and to me doesn't compare at all. (One day when I have more money I might splurge on some SE500's...but not now).
I have a LOD for my iPod already and the K701's. I realize I won't get the best sound out of them, but for now the portable is the best option. Rather than having a home amp that I would use 1/10 as much.