I don't really know how the 580's would do in a portable rig, as they're open and pretty big. Anyway, if you use the line out on your iPod, you'll bypass the internal headphone amp in its hardware. The iPod's headphone amp isn't the greatest, although it isn't the worst either. Still, it's much closer to the worst than the greatest. Anyway, you use the line out to connect to an amp, which will amp the headphones properly.