I have purchased ADDIEMs a couple of days ago, and had ample time to compare them with my Denon C751, so here's my two cents. I guess the best thing to say is that these two sets of earphones couldn't possibly be more different from each other. C751 look monstrous in comparison, heavy, dark, metal, as opposed to bright, transparent, and gentle look of ADDIEMs, and I thought it was funny that the sound output pretty much matched the appearance 100% in both cases. C751 have what sounds like an order of magnitude heavier bass than ADDIEMs, and at first I really thought that was the deal breaker, and that ADDIEMs are just not for me. However, I gave them a few days of listening, and I started to appreciate them more and more.
I started noticing that some of the more complex sound sequences, with bass mixing with strong guitars and voice, sounded muffled and mushy in C751s, but ADDIEMs always reproduced them clear as day, with a notable separation, clarity, and spaciousness of sound. I guess those dual drivers are put to some good use, where the single driver of C751 would mess things up when it had to reproduce sounds across the spectrum at the same time. ADDIEM bass wasn't threatening my inner ear, but I could hear everything really well instead, and yet bass was there, very controlled and nice sounding - just not very strong. Just as the bass sounds heavy on C751, so the highs just scream at you with them, whereas on ADDIEMs they sound more measured, and yet I actually think they are reproduced with better fidelity - I can notice some sounds in highs that I cannot with C751, which now actually sound like they could be distorting highs a bit. Also, as one would expect from the oppressive look of C751s, they tend to push the whole soundstage right into your head, whereas ADDIEMs have a lot more open and spaced soundstage. Even the silicon tips on ADDIEMs have much more gentle look and feel than those on C751 (which are more expensive earphones, let's not forget, or at least used to be when I got them last year). The silicon used is of much higher quality, and I found it created perfect seal with my ears, whereas C751 tips used hard, crappy rubber that I instantly replaced with somewhat better tips from my old CX300s.
Right now I am the crossroad where I should decide whether to keep ADDIEMs or return them for a refund, and I just don't know what to do. I really like how a lot of music sounds with them - for a recent example, I definitely prefer Goldfrapp's "Seventh Tree" album with them. Vocals and guitars really sound very clean and clear. I also like the remote/mic that works great with my Iphone 3GS, but that's not a huge factor. On the other hand, some of the electronic music and hip-hop just really fits C751s best. It's kind of hard to get into a real rocking mood with ADDIEMs, that you want to get into when listening to that kind of music. I cannot have both of these sets with me at the same time, C751s are big and somewhat impractical by themselves due to their heavy cable and mid-connector. I was toying with the idea of returning the ADDIEMs, and putting that money towards Klipsch Image X5, which cost about twice as much. Are they also twice as good though? Or even just as good? I've heard they have similar sound signature, but with a notably stronger bass, but I've also read from some people that ADDIEMs, due to their dual drives, sound better than many much more expensive earphones, which I can actually believe. X5 also cost about as much as I'm willing to pay for earphones, so X10, IE8, etc. are out of question for me. I am worried however that since X5s also use single driver, they could suffer from the same kind of problems as C751s, where complex sequences would sound muddled. Is there anyone here who could advise me should I get X5s instead of ADDIEMs?