I have very little experience with it. That's why I usually clam up. But I wouldn't recommend getting one that you can't return, as I've heard some crappy entry level amps.

You should still get an amp of some sort, the HD580 does get ...erm... less laid back (which I associate with more accurate) -- it requires less effort to hear details.

But the other thing you should do is practice listening. I use Sony MDR-7506/-V6's for monitoring, mostly because I am familiar with what it will do to the sounds that I record. Familiarity with the sound signature of your headphones is key. Listen to a recording that you're familiar with on speakers that you're familiar with, then listen to it on your headphones. Repeat to taste.