Well, I finally got a chance to sit down for an extended period with my C3s.
I have no buyer's remorse at all. These are excellent IEMs and well worth the money. As far as the review:
The first thing I noticed when I opened the package was the excellent case that is included with the earphones. It is both functional and sturdy, and it eliminates the need to buy another case(after all, these are quite expensive).
The fit and comfort is incredible. It took me about 10 minutes to first figure out how to put them in my ears, and then another 10 trying to get them out. And then, after 30 minutes, they started to get uncomfortable. I tried to twist them out, and *pop* they slid into place. I forgot that you have to give them a couterclockwise twist. Now they fit like a glove. With music on, I can't hear people talk in front of me. It's actually quite alarming when someone walks up behind me and touches me on the back to get my attention.
Now on to the sound:
The bass is full and deep, with great extension and volume. On tracks with extreme bass, such as Massive Attack's "Angel" and "Teardrop" you could feel the earphones vibrate a little with the power of the bass. There was (very) slight distortion at the beginning of "Angel," meaning that the extension may not be enough for the song, but overall it performed quite well. Some others have said that there is too much bass; I'm a bit of a basshead so I enjoy it. I haven't had to EQ these at all.
I feel that the high bass and the mids are where the C3s really shine. The high bass tones and mids feel in-your face and visceral. Some will prefer a more laid-back phone, but I don't. The immediacy of the music really makes my heart pump. The mids give the 'phones an 'aggressive' feeling, as EyeAmEye put it.
The highs are good but not great; I auditioned a friend's Westone 3s and their highs were definitely better. The C3s seem to be rolled-off. Honestly, though, I don't notice most of the time. The rolling-off occurs at such high frequencies that I didn't notice until I sat down to write this review. Despite the rolling-off, I don't think the C3s treble is bad. I'd say it is on par with the Shure SE530.
The C3s have a high level of detail. I'm currently in the process of rediscovering my music(again), and I greatly enjoy hearing things in my favorite songs that I had never heard before.
I listened to the 'phones unamped before I plugged in my BSG Cmoy. There's no doubt that the amp, even as basic as it is, drastically improved the sound quality. I wouldn't hesitate to listen to these unamped, but adding an amp improves the level of detail, soundstage, and eliminates much of the low-level hiss that comes with the sensitivity of the earphones.
I love these more every minute I sit with them. They are great earphones for the price, and the custom fit is excellent. If I could go back, I'd do it all over again.
Anyway, just my $.02.