This morning I received my UM3X which are meant as a backup when not using my custom ES3X's. Here's some quick impressions, but please bear in mind the custom ES3X's are a different, though certainly related, beast, so all comments and comparisons now only refer to other universal IEM's.
My previous IEM's include(d) Sony MDR-E888, Sony MDR-EX90, UE Super fi.5 v2 (2008), Shure SE530, and Westone 3, of which I've only kept EX90 and now the UM3X.
EDIT: Just a reminder I don't use an amp, and have a 160gb iPod Classic with no EQ. Same goes for all other IEM's and ES3X - I don't have my P-51 Mustang any more, and I only tried that with the W3 and ES3X and felt the Mustang + LOD did not provide better SQ than simply using the HP out.
The UM3X is the MOST balanced, NON- FATIGUING & comfortable universal IEM I've ever heard - I'm using the medium soft grey silicone tips that came with the W3 - I find (and found previously with my W3 & SE530's) the other tips uncomfortable and/ or painful. I'm using the same medium sized soft tips I used with the SE530s - with the W3's I used the large ones.
The UM3X is more comfortable, though not a lot more, than the W3 (and SE530).
Bass is brilliant and better, in my view, than on the W3 -- by better I mean more natural sounding, not so pronounced, and yet retaining clarity AND punch.
Fantastic mids - best, by far, from any universal IEM I've ever tried.
Highs are wonderfully done, NEVER shrill, and again, to these ears, better than the W3, and let me be clear - highs are NOT recessed at all, but simply not as pronounced as the W3, and certainly more present than those on the SE530 - simply superb!
Great sound/ head stage and instrument separation.
Have had them on for nearly 4 hrs now and have had no fatigue, a BIG issue for me with all IEM's except my custom ES3X's. I can even play my music louder than I usually do and experience no fatigue.
A better carrying case is provided with the UM3X's than that of the W3's -- it's a hard-shell case unlike the soft one that comes with the W3's - it basically protects the IEM's more.
As far as looks and finish go, the UM3X is smaller than the W3 and, as someone else mentioned elsewhere, the UM3X doesn't look as aesthetically polished and not as impeccably finished - maybe even stylish and hip - as the W3, but for this 'old fart' the understated, perhaps 'uncool' looks of the UM3X I find much more appealing -- Not ideal if you want to impress the girls (or boys) out there.
Cable is identical to that of the W3 - ZERO microphonics and wonderfully flexible.
You also get a warranty card which allows you to get an extra year's warranty (2 years' total).
Nice packaging, the only thing that actually looks cooler than the W3's - you easily get everything out the box in a few seconds.