I'd reckon the IE7 (the IE8 too) don't really need an amp. The latest iPod classic has a pretty good internal SOC amp which drives dynamic (that is what the IE7 is) earphones very well.
What you get with an amp (if you won't volume match them) probably comes from: placebo, and from volume (as you may not turn the volume up high enough with the earphones alone) which affects perceived dynamics.
The ear hears certain frequencies as they get louder and they disappear as the volume goes down. It is anatomy. The iPod should get way too loud for the IE7 and since the Classic already runs great resolution to dynamic earphones, an amp likely will only get in the way.
That said, even among amps: there are ones which can and ones which cannot drive earphones.
I'd stay away. Enjoy your combo now and if you are satisfied (as you should be), no need to rend a hole in your spleen for 'better quality'. If you want more dynamics, you can opt for 'acoustic' preset (which at loud volumes will clip), which is a basic loudness curve and will accentuate treble and bass, making dynamics better.
But always be careful of your ears. with dynamic earphones and a powerful amp like that in the Classic, I've never gone over 30% volume. Please be careful.