Well, I've had the CC51's for a week or so. I hate to say it, but I'm not thrilled. They have very crisp mids and they do have some bass if you adjust the EQ, but the main problem I'm having is distortion. When the volume goes up they don't get expansive - they grumble and get sibilant.
I didn't do a burn in period, but I've used them about 25 hours or so. The primary dissapointment are the lows - they sound canned and small.
Is this just a normal artifact of IEMs? Its my first pair and I had high hopes but the sound quality in these is really not exciting.