Pros: Superb bass, gorgeous mids, smooth-yet-sparkling highs, expansive soundstage, excellent imaging, very comfortable
Cons: Microphonics, no remote/mic included, short cord
The IE800 are the best IEMs I have ever tried. This includes the Shure SE846 & 535, Audeo PFE232, AKG 3003, JH13 and JH16 and many others. I also prefer their sound to many full size cans like the beyerdynamic DT-880, T70, T90; Sennheiser Momentum, HD650; Shure SRH1840 etc. The closest I've heard to the amazingly balanced sound of the IE800 is the LCD-2 rev 2, which I also own.
The critical thing to note is how cohesive and musical the soundscape is -- these excel with all genres of music that I've tried, from rock to jazz, acoustic to classical/orchestral, electronic to metal. It's laid back when you need it to be, and it can push out the PRaT like crazy when that's required.
The bass is full-bodied, with intense impact and extension but never encroaching on the mids. There is detail and texture regardless of whether it's the bass drum, the bass guitar or an electronic bass note. Having played acoustic and electric bass in countless bands and orchestras, I love the bass on these. The amount of bass on these is certainly more than 'neutral', but since they're probably going to be used in noisy environments, the amount of bass is quite appropriate.
The mids are engagingly lush and full-bodied, never sounding thin. Vocals are refreshingly realistic, rivalling the LCD-2. Guitars sound realistic and piano! Piano sounds spectacular with these. Having played piano since the age of 5, with a performance diploma under my belt, I can say these produce the most realistic piano timbre I've ever heard, save a real piano (and maybe the LCD-2).
And the treble -- don't get me started. They are so splendidly detailed, sparkling yet never harsh or sibilant. You can hear the smallest details in acoustic records; the movement of fingers along guitar frets, the shuffling of feet, the fuzz of piano string dampeners as the pianist pedals up and down. It's surreal. Adding to this is an expansive soundstage rivalling many high-end full size open cans, with pin-point precision in instrument separation and imaging.
The caveat to achieving such spectacular sound is in the fit -- when I first auditioned them in the store the tips were too large for me and the sound was quite sibilant. A smaller tip meant slightly deeper insertion and the sibilance disappeared and instead became sonic bliss.
To (very, very) briefly compare the IE800 to the following, mentioning the main reason for my preference of the IE800:
Shure SE846 & 535 -- these sound more upfront and almost congested in comparison, as there isn't as much soundstage depth and width compared to the IE800. I'm unsure what filters were on the SE846 that I tried.
Audeo PFE232 -- less cohesive sounding, less bass impact and body with slightly sibilant and artificial highs.
AKG 3003 -- way too much treble for my taste, tends to be quite sibilant.
JH13 (universal tip) -- very neutral and thus lacks the bass impact of the IE800 -- great for monitoring and use by live musicians etc but not as overall enjoyable experience, musically. Can also be sibilant
JH16 (universal tip) -- much bassier than JH13 but still produces noticeable sibilance at times. But otherwise a superb IEM, just very bulky (same goes for JH13)
Beyerdynamic DT-880, T90, T70 -- apart from two of these being open, the main sticking point is very neutral bass presentation, which means excellent transparency (at each price point), but lacks that punch and musicality at times.
Sennheiser Momentum -- brilliant closed cans but lacks PRaT and is very laid back, with somewhat loose bass.
Sennheiser HD650 -- quite neutral (and dark), very laid back
Shure 1840 -- neutral, quite similar to DT-880
Compared to LCD-2 rev. 2 -- the bass on the LCD-2 is renowned in its quality -- the IE800 has, however, noticeably more bass. But it still maintains excellent detail and texture even compared to the LCD-2. Mids on both are superb, with the LCD-2 ahead but not by leaps and bounds. With treble detail, I would give the LCD-2 a slight edge, probably owning to a slightly wider soundstage lending them an even more airy feel than the IE800 (which suffer in this regard by being IEMs, not open planar magnetic cans, of course! ). But of course, thanks to the IE800's isolating properties, it can be much more immersive than the LCD-2 when there are ambient noises, especially when coupled with their extreme comfort (LCD-2 pads are too rigid!); this makes the choice between LCD-2 and the IE800 for listening at home a harder one than one may think!
In everyday use, the microphonics can be quite distracting when walking, particularly at the Y-splitter/2.5mm jack, as it knocks against your chest. Any contact with the cable above the splitter also introduces significant microphonics. Unfortunately the cord is too short to go over-the-ear without being somewhat choked under the jaw. However, if the splitter is secured, there is minimal cable noise. Noise isolation is also decent, but not exceptional. I personally find it is a good balance between isolation and environmental noise awareness.
The IE800 are, however, extremely comfortable (given the right tips are used) and never tangle thanks to the Kevlar cabling. They also don’t suffer from the annoying suction effect that plagues most balanced-armature IEMs, as the vents quickly equalise with the pressure of the outside environment. It's just a shame that at this price Sennheiser didn't include a remote/mic cable like they do with the Momentum.
I usually run the IE800 straight out of my iPhone 5s and they sound great. Out of my desktop amp (Matrix M-Stage), there's certainly an improvement in bass response and soundstage, but given how incredible they sound out of a smartphone, there's really no need for a mobile amp, (cue outrage from you hardcore audiophiles out there! )
And to those out there looking at frequency response curves and waterfall plots for these, I wouldn't bother. They don't seem to represent at all the sound these produce in reality, since the IE800 are designed with a human ear canal in mind.
The IE800 are simply brilliant whether you're out-and-about and listening casually; at home and wanting to truly focus on the music; if you're monitoring or anything in between (except maybe during exercise, due to microphonics).
If I could only have one pair of earphones or headphones, I would pick the IE800. Every time. So, what are you waiting for? Go get a pair!