Well, I just got a pair of HD580s the other day and I found that the Mini3 drove it just fine...not as well as a full sized amp could do mind you, but it got the job done. I haven't spent a lot of time with it yet, but I'll listen a little more tonight.
Certainly the 580s sound much better from by Beta, but that's hardly a fair comparison to a portable.
i would think that any portable amp that uses a 9V PS or higher would be a good choice for higher impedance headphones...although I bet Justin's new Pico would drive the hell out of them as well. That little amp packs one hell of a punch.... can't wait to get mine