ZX1 has some really great bass slam. Bass is tight, melodic, tuneful where one can tell the differences between bass notes very easily. The Itouch individual bass notes is harder to define clearly and its get worst when the bass notes gets really low, it almost very hard to tell the diff at that point. The sound of Itouch is little on the thinner side in comparison and what it really lack is the attack. I don't see much of it while zx1's attack is pretty good. In general the Itouch will sound a little flat, pretty boring at times lacking some bass slam and attack.
To be fair, I am being very critical at this point where I listen to the same track over and over again to get that diff. I have also listen for hours on Itouch and then switch back to ZX1 on the same album. For most non-audiophile friends and relatives, they cannot tell the diff at all.. so if one is a causal listener then I would stay with Itouch. Its really good enough when not compared to zx1. For me, Once I know where the diff are, its hard for me to go back to itouch as I almost always notice it now even when I am not seriously listening to it.
To be able to say whether one is miles ahead really depends on the following example:
1) For causal listener, they cannot hear the differences even with an IEM like K3003 or Tralucent 1p2. (my partner is in this group)
2) For music lovers, they mention its only marginally better and at times, no differences at all (most of my friends is in here)
3) For audiophile perspective - there are differences but both is good enough
4) For very serious audiophile - There is alot of differences here and Itouch is an unacceptable DAP without an amp. These group can tell the diff between difference grade of cables and connectors almost 99% of the time.
5) Extremist audiophile/purist - haha! this group will say, burn the Itouch for it cannot exist to waste people lives hearing absolute garbage. This group can tell the diff between different formats of codec, like FLAC is better than ALAC and the differences between a 256 AAC and lossless is like day and night. They listen to test tones CDs and locomotive to test gears.. hahahaa..
6) supramundane audiophile: They say "I don't need to hear any of this and I already know the differences by its measurements and graph." They get a huge kick studying graph, harmonic distortion results, sine waves and by measuring tubes distortion, they already "hear" it all and no need to buy any...as they are able to form a mental image of the sound ....hahaha. (Ok I made all these group up
so I think it really depends on individual perspective... and for the sake of fun, joy and laughter, may I ask which group do you belong to - LOL