Pros: Strong, impactful bass, detailed mids, smooth but extended treble, details, clarity, imaging
Cons: Logo is easily wiped away, Y-split is too high up on stock cable. Stock tips are not optimal imo.
I'm going to write a new, proper, monster review of these later on. Just HAD to write something now. This is sort of in between my old review and my upcoming one.
Useful iem tips; Comply TS400/500, Auvio tips, Meelec Balanced tips. (All of these are better than the stock tips imo.)
The bass: Depending on tips, it hits hard, harder or very hard. My preferred tips are Meelec balanced dual flanges. They give the least mid bass impact, also the least bass bleed i.e., none to my ears. The sub bass is great and sounds realistic. Not overdone. The texture is great and bass guitars really shine if placed forward in the mix, however less so with the meelec tips. Using Comply TS400/500 (both fit actually) give a more closed in sound but it's still better than the included T400 (or 500, don't know). It brings a nice Comply-ish texture to the bass. More mid bass. More impact but more bleed. Auvio tips give the strongest bass response to my ears. They lack the texture of the TS500 but I'm fairly certain that Comply tips themselves imply a kind of texture/sound to the bass regardless of iem.
The mids: Here's where it differs the most. Again, my preference is Meelec balanced tips. With them the mids are quite leveled. The upper mids are just a tad smooth. Nothing that's getting to me really. I find the lower mids to be in line, not too warm. Male voices do not sound overly full or bloated. They sound really refined actually. They sound like I imagine a large membrane microphone sounds like. The detailing is really, really, really good. Until I got these, I craved the crisp upper mids of the CK100Pro that I borrowed and reviewed. The memory of them had really etched itself in my brain. Now I don't even consider buying them anymore. That's the Meelec balanced tips. The TS500 give a weightier sound. They sound fuller and more laid back. Less spacious and open. A bit more blurred but still top level details. The upper mids do get overshadowed by the lower mids, they don't have the same bite as they do with the meelec tips. Strings, brass and electric guitars sound a bit muted/dull/uninspiring/sleepy. Still better than UE900 and more presence than ASG-2. But it lacks that little bite that ASG-2 has despite it's overall darker tonality. Still, very solid choice of tips for a laid back listening. Auvio tips give the strongest bass response and the strongest mid bass which colours the mids. Some may like it. I find that the increased presence of the lower mids veil the upper mids. The treble is more present than the other tips and there can be some sibilance. Some prefer these tips, I like the more neutral meelec tips.
The highs: The highs are smooth, detailed, well extended. They aren't the airiest highs I've heard because they belong to the CK100Pro. But they are almost never sibilant. Great detail. With meelec balanced tips the balance between fundamentals and overtones in cymbals are very good. With TS500 there is a lack of fundamentals and the overtones are a bit muted. With auvio tips there is still a bit of fundamentals lacking and the overtones are stronger. My vote again falls on the meelec balanced but that's probably because I've figured out that I like to hang out just around neutral (but with stronger sub bass/lower bass).
Soundstage and imaging: Great soundstage and imaging. The claustrophobic feeling with T400(or 500, still not sure) that are preinstalled, is remedied easily with any of the other tips. Again, meelec balanced tips (<3). They give an openness to the soundstage and a better sense of air. The soundstage isn't as open as the IE8 (from memory) but the isolation, separation, detailing and everything else is just slaughtered by the FA-4E. I'd say that with a good source there is a nice 3D sound. Out of a smartphone it's mostly width [please insert name of iem that doesn't sound 2D out of a smartphone]. The separation is great and so is the placement of instruments. Switching to the ASG-2 does widen the stage a bit, could bring more height, I'm not sure. But it also tends to make the sound more Left-Center-Right. Instead of a nice panorama that fades into another part of the stage nicely.
Summary: The FA-4E is quite similar to the UE900, only better. I can't think of one single thing that the UE900 does better. Well, it's more functional with two cables included. Has a nicer case (the one that looks like you could pop a wedding ring out of it. And it does have sort of a more mainstream visual appeal to it. But the technical prowess of the FA-4E is a few notches over the head of UE900. The bass is tighter, the mids are more detailed and have a better texture/timbre, highs are pretty similar except that the UE900 does have a tendency to show sibilance in a few songs that the FA-4E doesn't. Fischer Amps has created a wonder. Or a monster. That's for sure. My hat off to Fischer Amps for creating one of the best universal iems regardless of price (more of a conclusion made from various posts in the thread) and one of the strongest contenders in its price bracket.