I want to first say that I've demoed/owned a lot of IEMs. I never seem to keep them longer then a month due to either losing them, them breaking or me just giving them away. This is why I don't list any IEMs in my profile. With that said I can't see the appeal of IEMs, well expensive IEMs. I've played around a lot with modding headphones and what I've noticed is the placement of the driver affects the sound more then any variable. The next variable is how shallow or deep the cup is on the headphone along with being open/closed. With an IEM you are drastically limited on the above variables. The drivers seem to be a consistent distance from the ear. There also doesn't seem to be enough room in an IEM to create a lively sound. I mention the above as physical traits that support my unimpressed opinion of IEMs. The highest end IEMs I've listened to was Sennheiser IE8 and I couldn't see spending more then $50 for it. It sounded very similar to the cheaper IEMs I have owned in the past.
I know this might come off as a rant/slamming IEMs but I assure it it is not. I've tried my hardest to like IEMs and I constantly seem to be disappointed. I've tried every type of tip to get a proper seal and even with that the IEMs I've listened to sound small and lackluster. My hope is that someone else has had this same experience and can mention a technique or something that I'm missing to get a "WOW" experience that so many people have when listening to IEMs.