I've used a pair with and without an amp. It is very high impedance and most say you can't drive it but I've tried and it worked fine. The difference with using it at a home stereo receiver was not significant, but you do have to push the volume higher than with most other headphones to get the same sound. Since I never use headphones full blast it wasn't that big a deal. They are usable.
But they come as 1/4 and you have to screw on an adapter for 1/8th. They seriously are not designed to be used with iPods for portable use. I strongly suggest you look to another model for portable use, if that is what you intend.
Also just pitching in my two cents, but I personally don't find the AKG 701s that good. I feel they are too expensive for what they sound like. But that's me. Just so you know, the kind of sound sig you will get is very flat, no emphasized bass for bass heads, treble doesn't exactly sparkle either. Good separation though and very clean.
Oh and they're *very* comfortable. AKG produces the most comfortable headsets known to mankind IMO.