Pros: Good bass, nice and warm mids, smooth treble, decent layering and sounstage. Appealing looks.
Cons: Very fit dependent, cable swivels and memory wire doesn't hold its shape. Doesn't feel like $400 iems.
First of all. I'm going to review these based on my listening experiences using a 100 Ohm adapter or from the Out2 of my BH. My pinholes are about 2/3 - 3/4 blocked. I'm using meelec balanced dual flanges and I have elongated the nozzle of my right housing with the tube from a comply TS500. For me that's the best sound I can get from them.
These feel like they don't need any formal introduction. As the follow up and replacement to one of the most renowned iems on the planet, the TF10, they have a lot to live up to. I've never heard the TF10. The UE900 were actually my first real iem-crush. From the moment I saw them I knew that I would buy them. With every review I read I knew that they were probably not the best price/performance and certainly not the best build quality for the price. Before I bought them I knew that I wanted more of a neutral sound with extended treble. http://rinchoi.blogspot.se/2012/10/ultimate-ears-part3-in-depth-analysis.html That link is probably what tipped me and made me pull the trigger. A choice that I don't regret.
Build, package, comfort: The included package is good. The best part of it is the airline attenuator. If you don't like bloated bass and veiled mids, it will be your best friend. Included tips are great if you can get a good fit. For me they're too short. I also don't fancy the comply tips with the UE900 as it takes away a bit of the treble extension from an iem with already smooth treble. Sonically I think that the small auvios are the best but fit wise the meelec balanced tips are in a league of their own. They are comfortable enough for me and once I have them in, they stay there but be prepared to do some tip rolling.
Sound: The stock UE900 I would describe as warm, bloated bass, veiled mids, slightly recessed but smooth treble. That's according to my preferences. But overall a good tuning for mainstream music. Very consumer friendly. The good part begins here.
With (partially) blocked pinholes and 100 Ohm adapter: The sound is mostly neutral but on the laid back and warm side. The bass is solid and not bloated or boomy. May not be enough for some. It's decent in speed and texture. Faster than GR07 but slower than something like R-50. There is a healthy amount of sub bass but less than both GR07 and R-50 but more than Re0. There is no bleed into the mids apparent to my ears.
The mids are smooth but still retain a good bite in electric guitars. They are pretty relaxed and a bit warm. Again I'd place them in between GR07 and R-50. Some might say that there's not enough edge to violins, higher pitched piano notes etc. I'd say that it's just right. Not dark, not bright, not grainy or edgy, just smooth but still well defined.
The treble is... smooth (surprise!) and well extended. It rarely exhibits any sibilance even in a bit harsher recordings. So a good balance and no glaring peaks. It lacks the air and presence that the Re0 has but it's way easier to listen to.
Imaging and soundstage is decent at the price. It's not the biggest sounding. I suspect that it actually sounds bigger without the adapter. But for me the bloat makes it a big no-no. A quality that the UE900 has is to place two instruments at almost the exact same spot but still separate them well. Maybe it's my ears that are untrained but I find it intriguing. The layering is decent at the price as well. It looses out to ASG-2 (especially if EQ'ed) which beats it in both soundstage size and separation.
Out of BH(2) Output 2: Now this is where it gets really interesting. Compared to the stock UE900 it's almost a u-turn. The treble becomes more present, the extension increases. The soundstage gets more hemispheric or circular. Within that sphere the layering is excellent. Then there's like an elliptical orbit of sounds. It's bigger than the more spherical inner circle. In between these two there is little to no layering. It's a bit like electron shells. (The simplified version.) The sound gets a bit colder and more analytical, the bass body disappears slightly compared to only 100 Ohm adapter. Now the good part is. If you own a BH(2) you don't have to block the pinholes which should bring the bass impact to the level of blocked pinholes and 100 Ohm adapter. The BH pretty much takes away the bloat and veiling without blocking the pinhole. This is a more aggressive tuning but the way the treble is presented is to my ears almost flawless. Detailed and with great presence in the upper treble but without the harshness.
Build quality (adjusted for price): 3/5
Handling (fit): 3/5
Stock sound: ~8/10
With 100 Ohm adapter: ~9,3/10
BH(2) Output2: ~9,4/10
The best quality that the UE900 has with blocked pinholes and 100 Ohm adapter is that it just sounds good with anything you throw at it. It's not extremely picky with recordings. It's not a sibilance monster. It's not a bass monster. It's just a good iem that lets you listen to any music you want to. It doesn't present it in any unique way like ASG-2 or CK100Pro do. For me as a Swede. It's just "lagom" (which means not too little, not too much, with an undertone of this is the perfect amount).