So I'm not super experienced with headphone stuff but I'll ask anyway.
Are you better off just getting the new hi-res Sony Walkman? or it won't independently provide enough power for many headphones? and this could double as a desktop amp/dac?
BeerCanChickenThere is one major advantage to this amp that would possibly tempt me to get it (given way more money) and that's the balanced outputs. Pretty cool on a portable amp, and probably a major reason why you would want it. The hi-res walkman doesn't have that. If you don't have balanced headphones then a Mojo might be a better choice for $100 less, new.
BeerCanChickenThe ZX2 Walkman is more than sufficient for earphones and efficient headphones (I happen to own one), but some full-sized headphones require more power than it can provide. Consider what you would like to pair with it before deciding either way.
As for the balanced outputs, the ZX2 supports a pseudo-balanced output (better signal separation and soundstage) that is a noticeable improvement with better earphones.