I agree with Plax, I have owned the westone 1 (essentially a um1), se215, and the PFE112 last. I regretted not listening to people who advised getting the PFE over other IEMs for the exact reasons Plax mentioned.
I actually found the sony ex-600 to sound very close if not a little bit more detailed to the k601s (ie k701). The ex600s have a very wide soundstage for an IEM which is what reminded me of the k601s in the first place. Unfortunately these do not isolate that well and my second jasonb's recommendation for a TWFK iem.
NB a TWFK iem is one that uses the knowles dual BA setup. These all come with a similar sound signature that for all intents and purpose sound like an...
There are some songs that are sibilant no matter what headphone you use. For example crumbs from your table by U2 (http://www.youtube.com/watch?v=MY5niA4eqmI) is probably the most sibilant song I have ever heard.