Everyone should always avoid presets, unless you know for a fact exactly what EQ curve is for the preset, and it just happens to match the deficiencies of your particular headphone's frequency response. Apple sucks donkey XXX for not having a customizable EQ native in the iPod app, but fortunately, with cheap apps like Equalizer and EQu, you can pretty much achieve anything you set out to do, unless you don't know what you're doing and create a distorted mess.
I have both Equalizer and EQu, and I have NEVER heard any distortion with them, and this is mainly because I know the do's and don'ts of EQ'ing. The key is knowing WHAT to do with parametric EQ's. If you don't really understand the relationship between the frequencies you're tweaking and the limitations of the drivers of your headphones, or how to precisely cater to that headphones inherent frequency response, then you will cause distortions. I suggest buying a good book on professional audio mixing and mastering techniques, and critical listening skills for pro audio engineers--they will make a world of difference on what you can do with EQ's. There are specific do's and don'ts when it comes to EQ'ing, and if you don't know them, you would be doing more harm than good. I suppose in this regard, for those who don't have the time or the interest to learn, ZO would be a quick fix, even if it's not ideal.
If you raise the gain to match pre-EQ volume levels it will distort. Fine, I get it, you don't like amps with bass boost. Noted.
Edit: This will be my last comment on this as Internet/forum arguing is pointless and self serving; and this one is full of condescension. EQ'ing isn't rocket science.
EQ'ing has it place. I used it successfully to fix the mid bass bleeding of the W3, as it was something that pervaded every song. The ZO has its place as well. When you are mobile and want varying levels of bass boost for different songs, due to the way they were recorded or mastered, the ZO is unbeatable. It is impractical to EQ for each song but it is easy and convenient to amp your phones current sound signature, adding just a bit more bass as you want it, when you want it.
I had wanted to add my own review and impressions with the ZO to this thread but I have no desire to continue arguing over the benefits of parametric EQ vs harware boost.
Edited by shotgunshane - 4/18/11 at 5:10am