Great review, joe. I've been meaning to comment on your review for a while, but never got around to it. While I mostly agree with your characterization of the UERM's sound signature, I'm surprised that you didn't seem to find the UERM to be qualitatively better at detail resolution and transparency compared to the JH16. I think it's true that the UERM's bass is much thinner than the JH16's, and its midrange and treble are more robust (and forward) than the 16's, but I don't think it's just a matter of the UERM having different frequency bands emphasized compared to other IEMs.
As I go back and forth between my ES5 and UERM, the first difference I notice every time is the increased sense of openness and clarity that the UERM deliver. The ES5 sounds significantly warmer and lusher, but also hazier and less focused. Imaging feels more precisely located, and the soundstage appears to be more 3-dimensional with the UERM. I sold my JH16s after feeling much the same way about them as I do the ES5; they are far more similar than different. The UERM is a totally different headphone altogether.
People seem unconvinced when I say there is a qualitative (and not just sound signature) difference between the UERM and the JH16 and ES5. Even my LCD-2 and Edition 8s don't deliver quite the same level of crisp detail. While some might find the UERM's presentation a bit thin due to the minimal bass impact, I think the UERM's bass output can vary considerably depending on the source and amp. A fairly neutral source and amp like the CLAS and Pico Slim allow the UERM to give razor-sharp resolution, but perhaps at the cost of bass presence. On the other hand, my warmest portable source, the HM-801, gives me the right amount of bass for most genres (and sometimes too much bass with the ES5).
I'm hoping to eventually post an ES5 vs. UERM (and possibly JH16) review, but it's clear to me that the UERM is the only custom IEM I've heard that was designed as a studio monitor. As a consequence, it doesn't have (as its default signature with most sources) the bass warmth that can help performers cancel out stage noise or feel the rhythm of the song. But it also provides the pinpoint accuracy that I would think studio engineers require.
In case anyone's interested, Craig from Whiplash is able to make one of his TWag cables using the UE prong covers. He took a pair of covers off of a stock UE cable and heatshrunk them onto one of his cables for me, and the result is a polished beauty that I hope will prevent the prongs from getting bent or being exposed to moisture.