They are nothing like I expected. I thought they would be incredibly bright, harsh, and lean. They are none of those. I would describe the sound as smooth and natural, "neutral-ish" maybe, with good body and very large. It's like going to the planetarium for the first time as a kid, or looking at memories in a photograph.
There's very little to no forward projection. This creates a very different kind of mental assembly of a soundstage. I "see" it very much like Eke's diagram, including the height he mentioned, but maybe shifted a touch toward the front rather than dead center. Center imaging is very lateral between the ears for images that aren't created/recorded with depth. Images are large but very liquid. They sound just very smooth, yet they can easily have a very nice edge/crispness. They render the crisp texture of electric guitars better than just about everything else I've heard save the GR07 MK1. The UERM always knows what to do smooth or crisp, and can do both. In Daft Punk's RAM it'll go buttery smooth like the 70's on you and when ZZ Top's Eliminator or Tron Legacy Remixed comes on, the guitars and beats have incredible crispness and texture. Except the smallest bit of sibilance on tracks already having sibilance, they are extremely inoffensive, yet somehow, they remain extremely engaging and dynamic.
The name of the game is refinement with the UERM. There is just a metric ton of finesse. It takes the crown from the W4 for being the most cohesive multi BA I've heard. This extends from top to bottom. There are only two issues to my ears: (1) there is a metallic tinge to the mid to upper treble and (2) the sound can have a slightly hollow aspect because of the very large images combined with a character that is just a bit thinner than natural, so everything has great body but lacks a but of fullness. I also suspect that some might find the soundstage presentation a tad but oddball-esque, i.e. very different from the standard forward projection people are used to. So moving on,
The bass is probably my favorite bass of an IEM to date. It is incredibly articulate. It has great body as noted above and is very very clean, creating more a feeling of sound than strictly weight/rumble/air pressure. Also, it does not affect the midrange in any way that isn't completely and entirely negligible to my ears. It also does something unique in my experience with IEMs and it is likely in part to do with the sheer vastness of the stereo separation and space: it's able to image bass more than any other IEM I've heard, keeping it entirely separate from images on the same plane to the left or right of it. It can throw a large bass cue dead center and have the sustain not reach the ears to the left or right. I also heard a bit less roll off than shotgunshane with usable subbass at 30hz. Past that it rolled off quickly, but I didn't find myself missing it at all, which kind of surprised me. Interestingly enough, this is the only IEM in which Limit to Your Love by James Blake doesn't sound absolutely aweful and unlistenable to me.
The midrange is neither warm not cool. Some might call it sweet but I'd liken it to natural. Voices sound very much like you would expect them to sound like. They aren't nasal, or harsh, or thin. To can easily forget about them that way and let go into the music.
Instrument timbre is generally goodie good. Like has been said, there's a bit of a metallic tinge to the upper treble and this hurts instruments like cymbals and bells. Horns are generally good but not quite as aggressive and crisp as on the IE800, which was a particular standout for me. Drums have good body and reverb in general. The violin particularly stood out for me as exceptional. It was organic and rich and smooth. Other IEMs tend to make violists sound a bit squeaky and nasal. Piano was interesting in that it was diverse. The F111 for example is "always on" with piano's making them all sound rich and lingering in harmonics but the UERM while a little glassier at best, could diversify more between different kinds of pianos and playing styles. There was just more delicacy and finesse.
There is a small bit of sibilance on very hotly mastered recordings to my ears, though slightly less than the 1Plus2 and more less than the ASG-2 and IE800.
I also want to point out that the tuning of UERM is incredibly wholistic and cohesive in regard to the separate frequencies ranges and their interactions. My previous benchmark for multi-driver IEMs was the W4 but this is a bit better in my book. The tuning across all the drivers is also incredibly consistent.
My previous benchmark for transparency was the 1Plus2. And after hearing the UERM that hasn't changed, per se. It's actually created another benchmark for me. While the 1Plus2 is the most transparent IEM I've heard in regard to gear, the chain it's connected through, the UERM is more transparent to the music at the end of the chain. I listened to two metal recordings that came from studios in California made at around the same time, and with the UERM, not only could I discern the slightly different effects pedals being used on the electric guitars but I could also clearly hear the difference in the studio and recording layout. This was a revelation to me. Usually, my comment with these recordings is that "yup, they sound like California metal alright," but with the UERM they sounded like individual bands, with individual identities and very distinct yet only minutely different takes on the same musically temporal ideas.
The TFRM (modded TF10):
I don't know how the TF10 originally sounded. I'd never heard it so I don't know how much has changed. But, if the fit was as finicky as the TFRM, then it would likely have never seen the light of day in my house after the first week. Before I moved onto some not included tips, I was ready to give the TFRM a 4 out of 10 in similarity to the UERM, at best. I was very unimpressed to say the least, and had almost given up. Whenever I actually positioned it just so, so that it wouldnt sound like the sound was entirely imaged 2/3 to either side of the stage, it sounded like a tiny harsh mess.
Also, I'm convinced that Inks' picture of the TFRM fit is very very photoshopped. Either that or we're dealing with a stone that might better be left unturned.
I finally got an consistently good sounding fit for my ears with a set of Auvios.
In trying to mimic the performance of the UERM, created is a mismatch between the new design and original intent. The new parts just don't mesh well with whatever is left over from the TF10, like how a body might reject a donated organ, no matter how good. And because this might sound a little harsh since I'll be going into differences, I just want to be up front and say that Rin did a fantastic job with this. The TFRM in its own right sounds very good and I would easily put it up with the best I've heard in the lower price ranges of upper tier sound, ie below the magic five oh oh.
On sound signature alone, I would rate the similarity at a solid 7.5, maybe an 8 if you can get that magically elusive reference plane fit and not need to have them surgically removed afterward. But the devil is in the details, and it's in the presentation and refinement that the UERM pulls away, and it pulls hard. The TFRM exacerbates many of the UERM's flaws while not quite meeting up to most of its strengths.
Where the UERM already has a metallic tinge to the upper treble, the TFRM has even more, and it is spread wider, creeping it's way into the mids. This is not helped by the TFRM being generally harsher than the UERM. It's a much denser sound, and combined with the added harshness makes some songs a little hard to listen to.
The density of the sound is wholistic, from bass through upper treble. In that way, even though the bass reaches a bit deeper, it lacks the body of the UERM sound. It's fuller down low, but not more satisfying for it, and thinner up top.
The UERM has a much grander sense of scale, larger images, more body, larger stage with more stereo separation and cleaner imaging and more clarity, which is interesting because the TFRM is generally harsher and more aggressive. All the while, it just isn't as dynamic. The images on the TFRM just aren't as palpable.
Finally, it doesn't have the sense of transparency to the recording as the UERM. I think this is in large part due to a very scientific principle I call "finesse." The refinement and finesse of the UERM allow it to tailor it's presentation, sharp and crisp with one track, and soft and smooth with the next. The TFRM just doesn't have this range to keep up.
Now in regard to the overall similarity of sound, I would say, with an amazing fit, I would give it a solid 6. With a perfect fit, who knows, but I'd only 3 people in the world can achieve a perfect fit, does it really matter?
Because I'm not really sure about the value proposition as I feel something is worth whatever someone is willing to pay for it. I'd be willing to pay a bit less than retail for a UERM and since I compared the TFRM to <$500 IEM's I've heard earlier, I figure 2-3x seems appropriate for me in how much more I would pay for the UERM.