You know, there are times when I try the K81Dj's and I like them better than the K271S. I think the reasoning behind that is because they have better bass than the K271S, although I'm going to have to say that they can't quite match the sound clarity. The mids are nice and clear and the highs are rolled off, just like the K271S. I think the reason I like them is because they're so much like the K271S but with better bass. Sure, they clarity isn't as clear, but they're not that much worse.
I really find that they don't need to be amped to sound great. The bass gets tighter and everything sort of spreads out with amplification, but I've come to realize, after using my Hornet on the go, that I really don't like carrying too much around when I'm walking to and from class. I've been using the K81DJ's unamp from my iPod and I like it just fine.