First of all, after spending countless hours avoiding work reading this site (and attending/exhibiting at can jam '08) this is my first post.
Just wanted to relay the experience I had with the CK7s that I just got last week. Of any canal phone/IEM I have listened to, I have never listened to anything where the sound quality varies so profoundly based on seal/tip used. In my experience, the tips that come with the CK7s are horrible.
After burning the CK7s in with pink noise for about 10 hours, I was worried about how shrill the highs were, how the vocals had sort of this dreamy wash over them, and how the bass was virtually non-existent. They were really fatiguing and sounded almost on par with generic drugstore/airplane ear buds. I was using the largest silicone tips that come with the CK7s because I thought I was getting a decent seal, and I had used the largest sized tips with my previous canal phones (akg k324p) and anything else I had ever demoed. So I decided to try the medium tips instead, and dear lord it was a night and day difference in sound quality. All the positive things everything says about the CK7s just started to bloom; the sound became big, neutral and detailed, the treble began to sparkle (and was no longer fatiguing), huge, but tight, bass appeared out of nowhere, and the imaging was really impressive for an in ear headphone.
Then this morning I was getting a little frustrated with the medium tips because while I was able to get a seal, as I have big ears it would often slip if I was walking around, so I decided to tip swap with the large k324 tips I had. With the k324 tips the sound I got was appreciably better, which didn't make a lot of sense as they appeared to be an identical size to the large CK7 tips (maybe *slightly* thicker silicone, but that's it), so just to experiment I switched back the large CK7 tips, and sure enough the sound went back to being shrill and anemic. So if you get a pair of CK7s, I seriously recommend tip swapping and trying different sizes until you get a perfect fit, because once you get a good seal, these things sound so much incredibly better. Also, I can't understand with the shape of the titanium casings how anyone could get a good fit without wearing them over the ears.
I have been driving them with a tomahawk and using a 50 ohm impedance adapter and they just sound absolutely beautiful, and I couldn't be happier.