Bump:
background: I used a set of ER-6s (not the "i"s, but the regular ER-6) for a long long time. Big fan of the bi-flange silicon tip. I agree that the microphonics of the cable reduced it to sitting (which I primarily did) and it's sort of a bright listening device. That said, my left channel seems to have died, so I picked up a set of UM3Xs from Westone.
For those of you who are familiar with the ety sound, the UM3X is designed as a stage monitor, and has much more of a flat or unhyped response then it's cousin the W3. Over the evening, I noticed that there is less 6-12khz response compared to the ER-6s and there is bass (lets say, +4db worth and the extension is lower as well). Midrange is recessed a bit comparatively, with the lower the khz, the less recessed. It would bother me since I like that laser precession of the etys, if this wasn't so good... The soundstage is the other general difference. The etys have a flat or in-your-face soundstage. If your into that sort of thing, there you go. The UM3Xs have a much bigger soundstage. The easiest example is setup a band on stage. Half on your left and half on the right. Now stand on stage between them and listen. Thats the etys. Now step back into the audience by about 10 ft (so maybe 3rd or 5th row in a small club), thats the UM3X soundstage.
Couple of general points:
1) The etys have laser precision. The westones are detailed, but not in a precise manner. There are things I hear on some recordings, that were more difficult to hear on the etys. Overall, comparing the two, the westones appear slightly veiled, but less so then regular headphones would sound veiled. The UM3X does seem to have a neutral sound, slightly warm, slightly dark compared to the etys which were generally regarded as bright and sterile. Areas where I don't recall hearing much bass, I don't hear in the UM3X listenings, while tapes that were bass heavy, *are* bass heavy IMHO.
2) If you like foam tips, the UM3X is great, if you hate comply, then when you buy them, look at getting the $120 UM-56 custom mold adaptor (these don't fit your musicians plugs like the ER-6s). There are no other tips delivered stock, but supposedly the same aftermarket tips for the Shure 530 will work as they use a similar nozzle end.
This is ultimately why I think I'll keep the UM3X and get the UM-56 adaptors:
3) When I wear my musicians plugs, I get a little more bass then I would otherwise. I'm glad to wear the plugs and things are fine, but i get a little more bass then otherwise. This IEM generally replicates that better then the ety ER-6 did. Now, I liked the ety, it was a great IEM, however this is closer to what I hear at a show while taping (for better or worse).
edit:
I hate comply. f'ing foam BS... I get a consistent fit or balanced sound about once every 10 or 11 tries. I called my audiologist today and will get impressions when I get back to town on Monday.