I've been a recording engineer and studio musician for over 30 years. I've mixed hundreds of albums, dozens of feature movies and tens of thousands of TV commercials. I listen for a living and have a very critical ear when selecting monitors and headphones.
I use 4 different sets of headphones for different application. The Triple-fi's, custom molded UE7's, Bose Tri Ports, and yesterday I got the Logitech UE 900's. Here's my take on the UE 900's vs. the Triple Fi's.
The UE 900's have a noticeable bump at around 7K with a very narrow Q. So much so, that it brings the hi hat (and cymbals) too far forward in the mix for me. I'm all for brightness, but what bothers me is that it's not a smooth brightness. It's kind of grainy or harsh. They are also lacking in the mid bass area. (150 - 400 hz) I get (barely) enough thump from the kick drum, but once the bass player gets off the low E string the bass line kind of goes away. That's a problem, I want to hear the whole bass line. Overall, they make me want to reach for the EQ button and that's never a good sign for any monitor or mic. On the good side, they are very light weight and comfortable to wear. They seem to stay in your ears better than any other (non custom molded) IEM. They look cool in your ears, and I love the mic on the cable. I'm not so sure about the braided cable. Time will tell if it gets kinked up or not, but my gut tells me it might. Great packaging, great extras, lots of choices with buds. But ultimately they don't sound as accurate as the Triple Fi's to me. I think they are good for casual listening, working out, especially cycling or snowboarding because of the low profile and less wind noise, but I would NEVER use them to mix with. I'd go with the Triple Fi's because they are closer to studio monitors or the Bose Tri ports because they are closer to what most consumers want to hear. A headphone with a permanent loudness button on. OK headphone snobs, you can laugh now about the Tri ports, but honestly as a mixer, I always check my mixes on them to make sure I haven't over cooked the top or bottom.
The Triple Fi's are great and very accurate. By accurate I mean closer to studio monitors. No hype on the top or bottom, just a very well balance sound. The fit is a little weird and of course you could never use them on stage as a musician or you'd look like a total goof. The only way I got the fit to work for me was Comply foam tips, and going with one large tip, the other medium. But now the fit is great and they stay in my ears no problem. I've mixed many, many projects with these headphones and know them well. I prefer the sound of the Triple Fi's to even my UE 7's and often use them at home while practicing or programing parts. But never while playing a gig.
As for the UE 7's. They are a great entry level custom mold IEM, but next time around I'll probably go with the Capitol Studio ones. The UE 7's are on the mid rangy side and really lack the low bass. Eventually I'll need to get a new pair of custom molds, but I keep putting it off because of the money.
So there's my 2 cents. If fit and look is important to you I'd get the UE 900's. If sound quality is more important, I'd get the Triple Fi's. If you are a musician thinking to cover performing IEM's by getting some off the shelve UE 900's I'd say save your money and get custom molds. You need them when playing live or during long rehearsals. When you sweat, custom molds always stay in.
Hope this helps someone.
None of the above are truly neutral. 