I know this is way old but I will likely be downgrading my desktop HD800 rig (changing jobs) and will probably move to IEM's.
When I owned the SM3, I really enjoyed them for what I felt was their best strength - vocal rendering. Particularly with female vocals I found them to be very enjoyable. That said how does the 900 compare with respect to vocals? Are they equally front/center stage as the SMW or more pulled back like something from Shure? The last UE I owned was the custom UE10 which I loved.
Here are my quick comparisons of the UE 900 sourced by the DX100 with triple flange tips on the UE 900.
Vs. TF10: With the V shaped sound signature, the TF10 contrasts with the UE 900 as the UE 900 has a better balance from top to bottom. The TF10 is warmer, but the bass quantity between the two isn’t too far off while the TF10 has a bit more treble that is more sparkly/peaky. What’s not to like with the UE 900 vs. the TF10 as it is cleaner, clearer, more realistic and convincing while presenting more detail and fitting better. Definitely a step up, and if you want the TF10 V shaped sound you can just EQ the mids down a bit!
Vs. SM3: The SM3 is much thicker and warmer with less clarity and much more bass emphasis and power. While the treble of the SM3 doesn’t sound lacking, it isn’t as extended or present as the UE 900. The UE 900 is more open and spacious with better articulation of details within the presentation. The balance across the spectrum of the UE 900 is much better and while the SM3 has great imaging, the UE 900 bests it. Overall the UE 900 has a cleaner, clearer presentation. I think the form factor of the SM3 is a bit easier to use for my ears, but the UE 900 is still very easy to use and comfortable.
Vs. custom TF10 with silver cable (note that the sound isn’t exactly the same as the universal TF10 and the aftermarket cable makes a significant difference to the sound): The UE 900 has a more mid-forward, bright, and spacious/3D sound than the TF10. Bass quantity between the two is quite close, however with really bass heavy tracks the customized TF10 outputs slightly more deep bass rumble (note that the universal fit TF10 also has less bass rumble than the customized one). Detail levels are higher with better instrument separation and resolution within the presentation, with the ability to articulate soft and distant sounds within the soundstage in an easy to hear way. Overall the UE 900 is a step up in terms of resolution, detail, soundstage, and has a better balance across the frequency spectrum. My custom TF10 review.
Vs. UE IERM: These two present music in similar fashion, in a spacious and 3D manner, but the UE 900 is warmer/fuller and has more bass focus and a bit less treble. The treble of the UE 900 is more forgiving, but along with that some of the IERM details get lost in the smoother presentation. Spatially, the IERM presents a space that is larger than the UE 900 in all directions, but retains the same proportions giving a very similar feel. The IERM is the choice if you want to hear ultra-high levels of detail and have a very large presentation space, but the UE 900 is a relatively close approximation with a more “consumer” sound. My IERM review.