I finally got a chance to get to the Apple Store and demo the Amperiors and I was not impressed. As a long time HD 25-1 II owner, I thought perhaps the lower impedance of the Amperior would offer ampless the sound of the HD 25-1 II with an amp, which I believe is Sennheiser's intention, thus the name: Amp-erior. This was not the case however and the Amperior to my ears displays the same muddiness that the HD 25-1 II suffers without an amp. That's not to say that the Amperior sounds bad, but I believe one's money is better spent buying the HD 25-1 II and an amp. Along with the much cheaper price for the headphones, the higher impedance of the HD 25-1 II means that they will see more power from the additional voltage offered by an amp than the Amperior would. For those interested in the quality of the sound, I believe the HD 25-1 II with an amp will always better the Amperior, aluminum capsules and smooth velour pads notwithstanding. YMMV.
About a year ago when I was in an Apple store, I had my HD 25-1 with me, and just out of curiosity I thought I'd try the HD 25-II that was on display in the Apple store. To my surprise the HD 25-II sounded muddy and boomy next my well-used HD 25-1 which sounded much clearer and refined (both were fitted with pleather pads and stock cables), so my guess is that brand new HD 25-II's - though they sound good straight out of the box - require some burn-in to sound at their best.
I won't comment on amping, and FYI: I used the above headphones straight out of my iPhone.