It becomes less of a "need" thing (as if there's really a necessity within this hobby - it's what you make of it) and more of a "want" thing. As in the want for different sigs. At some point the fine line between usability and incremental improvements get blurred.
It's absolutely fine if people want to get into it as it's their prerogative/preference. But it's absolutely not fine to make it out as anything other than personal preference. Rumors of audio nirvana from a $500 magic box are greatly exaggerated.
I've personally had enough portable amps to not care enough where I'm at the point where I've only kept an E5 and a E11. And the latter really sucks. They all really suck. Value is a moot point but the only ones I've heard as of recent that can be justified in terms of practicality and feature sets, are, guess what, the C5s and the UHA-6S MKIIs.
So when people come to me to ask for amp recs I show them the door as I can't wholeheartedly put a recommendation into something I don't believe in anymore.
That being said the bass on the FXZ200s are almost heavy enough to wash out the mids :P
I've followed the preamble on the CKS1000 thread with the graphs and the ink and the bok choi and the burning flames of purgatory. Just me stating an opinion but I'm inclined to side with the graphs at this point. No I'm not making them out as an absolute, merely a reference point. But the FR curve, in this case, correlates nicely with what I've heard out of the 1000s. Not that that's bad. They are stupendously textured and powerfully fun IEMs. So I look at it all in a positive light. And of course spectral decay, THD, haven't been brought out yet. So it's too early to say anything yet as it is.
Again, just an opinion amongst the sea of arseholes.
Crisp, decent low-end presence, AD700-reminiscent (keep in mind that I'm on the AD700-is-horribly-anemic side of the argument so take my reference point with a grain of salt) - well...
I'd think twice against anything in your choices other than maybe the K2 (which I haven't heard, only going by general impressions by others at this point). The 272s are too rounded of note to be considered crisp, UM3Xs are aggressive in the warm and powerful sort of sense, GR07s have the dynamics and edge on each not but they'd probably end up too bassy, the SE535s are extremely dull of note in comparison and just too mid-forward from what I'm assuming you're wanting. And have not heard the Alclairs.
Have you looked at the UE900s yet? Very crisp, bass presence is there and very linear and clean. Seems to mess well with your criteria, but with way more extension than the AD700s.
I had not ill look around for them aswell, any others you can recommend?