Quick Review of the Denon AH-C751's (as compared with X3i's)
I got these a week ago, burnt them in for about 24 hours, and I've tried them side-by-side with the X3i's with the Sansa Clip and Zune 80, using some Roots, Aesop Rock, Miles Davis, Alice In Chains, Cat Power, Thin Lizzy and Nick Drake to compare.
The Denon AH-C751's (esstentially the same as the C700's) retail for $199.99, and even on sale on Amazon right now, are more than twice the price of the X3i's. Compared to the X3i's, these are more balanced earphones, the bass is not as emphasized, but that's not to say it's not there, it certainly is, and the quality of the bass is great, just not as much quantity. The highs and mids are noticably more clear and present than the X3i's, the mids are where these phones really shine, vocals and acoustic instruments sound excellent. I did find I prefer the X3i's for some genres that the C700's might be a little too bright for in comparison, like Hip-Hop. The sound alone may not justify the price jump over the X3i's, but combined with the build quality, they're worth the extra, these phones are made of spun aluminum, they can take a beating, and the cable seems to be of good quality. These don't go as deep into the ear canal as the X3i's, and they're larger overall, so they don't isolate as well and you can feel some additional weight, but overall they are comfortable.
As a side note, I have even greater respect for the Sansa Clip now, as I can hear the superiority of its sound quality even more so with the C700's.