I thought I would add what I can to this thorough thread. I recently received a set of C700s as an upgrade to my Creative EP630s and have put in several hours on them. I had some concerns about buying the C700s and figure I can try to address my impression of these areas. The major concerns I had when choosing the C700s were their size, weight, isolation and "excessive" treble compared to the common CX300/EP630, so that is what I will be focusing on here.
As some background, I listen to a wide variety of music but mostly indie rock, classic rock, classical music, ambient, electronic, and a bunch of other genres less often. I'm (usually) not a huge treble fan - I find it to easily be fatiguing. I used Shure E500s/SE530s for almost a year and think that their sound is pretty much perfect. I had no problem with the rolled off highs of the SE530s. But they were overkill for my purposes, which is mostly unamped traveling listening. I sold them off and was left with just the EP630s that just aren't cutting it. I wanted another, relatively cheap set of phones that I can take anywhere and be happy. With the EP630s, the bass is bloated and severely lacks detail, highs seem sharp and artificial, and the instrument separation is nonexistent. They simply are not much fun. Plus the cable sucks on them and the isolation is pretty low. But they are highly portable, easy to drive and cheap. They will likely still be my gym and running phones for a long time. I used to have a decent source (Emu 0404 + fully loaded pimeta amp), but now I have a Samsung T9 and iPod nano. I mostly use the Nano since its so much easier to use and has better capacity and battery life - the T9 has better sound though.
Anyways... on to the newly arrived C700s (which were bought used). I chose the C700 for their reported bass, clarity and fun, engaging sound. The cable really is great. The length of it is prefect for me and being one whole piece (as opposed to the SE530s) is a huge plus since I dont use an amp. I was actually surprised to notice that the cable length is the same as the creative length since its seems about 1 foot shorter for some reason. Its just easier to manage. The construction is solid although I do still have some reservations about the open back on them since it seems to invite rain and moisture. The earpiece weight is a tad more than the the creatives, but is not noticeable when worn. They do have enough weight to get some momentum when swinging on their own. I wear all earphones cable-over-ear to reduce microphonics. The C700s stay in place much, much better this way than the creatives. Microphonics are present, but hardly annoying this way. The canal fit is ever so slightly harder to get correct than the creatives due to a larger 'barrel', but nothing worth complaining about. None of the supplied tips fit my canals so I have to use the tips from the creatives to get a good seal. They do stick out a bit compared to the creatives (see pictures for size comparisons), but not enough to be a nuisance when wearing a toque. Its also nothing I'm embarrassed about and I have small ears compared to most people (normal size canals, though... I use medium silicon tips). Isolation is a lot better than the creatives - not so much for how much they filter out, but what they filter. They filter out low and mid frequency noise much better than the creatives and filter high frequency noise slightly better. I can't hear myself type with them on nearly as much as I can with the creatives.
Physical comparisons:
[following a head-fi trend I did not shave before taking pictures]
As far as sound goes, my first impression after switching from the 630s was "Wow. That's a lot of treble. I hope I get used to that" and at the same time "Oh man... that's really nice". I quickly lost this treble anxiety as I noticed just how much I had adapted the highly veiled presentation of the EP630s - they sound like a piece of plastic has been put over the top of the speaker opening. The bass extension and detail is very good but if I had to nitpick, I'd say that the upper bass can roll over the lower mids a bit. Nonetheless, the bass is really enjoyable - maybe less so than the SE530s, but these have a different bass presence. I'd say its more speaker like than the shures. As said by others, the mids are great, although a bit recessed *compared to the bass and treble* - which is what these shine at. The treble is... awesome. Maybe I've never paid attention to treble much before or purposely bought "veiled" headphones to avoid it, but I have never found treble so enjoyable as I have with the C700s. Cymbal hits give me shivers. At high volumes, though, the highs can be fatiguing. I haven't worn them for several consecutive hours to say whether this happens at mid/low volumes as well with extended listening, but I'll update this when I do.
Small complaints: the soundstage is not overly impressive and fast, complex music can seem a bit compressed compared to SE530s and many full headphones. I wish I'd had some DragonForce before selling my SE530s because I'd love to A-B them with the C700s to get a better feel for their PRaT. On the Creatives 'through the fire and flames' is a confusing onslaught of noise. The C700s make it fun and comprehensible but the limited soundstage takes away from the overall presentation. However, for canalphones and/or IEMs, this will (almost) always be a trade-off for isolation and portability. I'm satisfied with the soundstage of the C700s.
I think the C700 are a perfect upgrade to the creative EP630. After almost three years of head-fi I understand how expensive 'partial' upgrades can get since they never stop. I figured these would pretty much max out the potential of my mediocre source (unamped DAP) and they do. Without a new source, amp, and headphones, I don't think I can substantially improve what I have. Overall, they are different from the SE530s but I've been enjoying music almost as much as I did with the Shures.
Update after a few more days of use:
I think I need to update my impressions after using them for a few days with a nano. The treble can begin to sound a bit splashy and overbearing after I use them for several consecutive hours. The soundstage compression and lack of instrument separation is a negative for me and can even be a bit disorienting at times. I loved the separation of individual instruments with the SE530 (that soozieq discussed) and these do not have that at all. These faults only appear with certain types of music, though, and I'm sure many people would not find the same thing.
That's with an iPod nano 2g headphone out. I hauled out my pimeta and tried amping the thing - there's is a large improvement in all areas of sound and presentation. The C700s are power hungry little things... and I guess that makes DAP pairing critical for these headphones. I've been through this before with akg K271s and know what amping can do for some headphones, but I've never been a big advocate of portable amping since the improvement is usually not worth the extra nuisance. The C700s are an exception to this rule. So I picked up an iBasso T2 off another head-fier today and this seems like a very good solution for sound and portability (I'd rather not buy yet another DAP), but I have limited experience with it so far and can't comment on specifics. I also do not yet have a LOD so I just use the headphone out for now.
So...there's hope that the fatigue can be beat and I can keep them. But regardless of the amping improvement, my opinion of the C700s have been tempered a bit since my initial impressions. I am still not a huge treble fan, although these do treble very well. They have a sound and presentation that I can't 'escape' when I'm wearing them: its bright and sparkly with tons of bass and right inside my head at the forefront of my attention - and I realize that I'm not always in the mood for that.
Final update after 2+ weeks.
Still very happy with the amping improvement. After two to three weeks of using these everyday I can say that I have fully adjusted to the sound of the C700. My portable setup (2g nano+T2+C700) is insanely small and extremely good. There's likely a better match for C700s than the T2 (which can roll off the highs and bloat the bass a bit), but the size of it is perfect. This is probably the best portable setup I have owned. Definitely keeping these.
Looking at my last update, I'm fairly certain that I found the C700s 'inescapable' because I had them too loud to overcome background noise. I've adjusted to it now and can block it out with lower volumes. The isolation of these is not that great, but I actually like hearing some of the outside world now. Like cars.