[antonyfirst]

Stax SRX MkIII Pro: almost dead neutral, some resonance (2-3 dB) at 3kHz. Very extended at both extremes, not sibilant unlike its normal bias version is said to be. Revealing to source's tonality and any digital glare. Small soundstage, sharp imaging, fast, when underamped lacks some bass transient control and percussion resolution. Very uncomfortable, original cable is microphonic, as well as the grilles, potentially distracting.

Stax SR-003: warm. Lacks deep bass, there is some emphasis on midbass and lower midrange, but no bloat à la Westone 3. Small soundstage, extremely high resolution, details presented in a relaxed way. Lacks treble energy (meaning it's recessed) and it's not perfect for rock music. Manages to hurt your ear canals. Stock tips are the only good sounding ones to me, but Sony-like biflanges can be adapted. The headband suggests to be a tortureinstrument invented by a sadic dentist. Without the headband, the earphones are likely to fall while moving.

Apuresound ER4P: addicting, emotional although not neutral. Bass is still on the light side, but is improved over stock ER4P, there is depth, and some early midbass emphasis. Bass is fast, well defined, tight resembling how a stone would hit. Midrange is what makes this tweaked headphone more unique. Especially prominent with foam tips, the 1-2 kHz is emphasized giving many vocals the main role, making for a more "live" experience and great intimacy. It can be a drawback with trance and especially classical. while being vedry different genres, some instruments/samples sound shouty through the "midrange hill".
Treble is delightful, as the peak proper of the stock earphone is completely flattened. Flattening the midrange would help in perceiving bass strength, already bettered over stock thanks to the reduced treble (which is overwhelming and sibilant in stock etys). Small soundstage.

Westone 3: deep bass, bloated upper bass and lower midrange with triflanges. Better fittings, to my knowledge, reduce the hump to listenable levels, otherwise there is need for EQ. Midrange over 2kHz is tamed and makes for vocals a bit distant.
Treble is pretty linear up to 10 kHz, while lacking crispness over it.
Poor fittings (usually short tips) make everything sibilant, thin and distant. Big soundstage.

Klipsch Image X10: bass is big, deep but boomy although not bloated. Midrange is warmish, without any particular emphasis, but present. Treble lacks resolution. Pretty big soundstage for the size, especially seeing how deep these go inside the ear.

Denon D5000: head-rattling bass, horrible treble ("snakes in your ears"). Sibilance is continuous, painful and unfixable by potential markl mods. Huge soundstage even from a portable amp. Heavy to wear, although not discomfortable.

Audio-Technica Ath-ESW9: strong clamp. No isolation although the design is closed. Not really portable for walking or commuting. Mid/upper bass emphasis, lush midrange, recessed middle treble resulting in forgiveness to sibilance and insensitive to more detailed sources. Small soundstage for the size of the headphone.

Yuin G1: clipon that is more isolating than an open earbud. Huge soundstage, weak bass, very bright tonality that can be very emotional, although occasionally sibilant but not too brush.

Yuin PK1: gradoish, strong bass, midrange prominence that make most rock colored in a similar way. Big soundstage. High impedance (150 ohm), needs an amp.

Yuin OK1: different from pk1. Higher level of detail, neutral bass and midrange, but there is a noticeable peak over 6kHz that helps in bringing more details, while adding sensitivity to sibilance. Extreme frequencies performance: treble is very extended, while bass lacks depth. Big soundstage for an earbud. Awesome imaging. Supreme comfort. Would benefit from a tubey amp.

Yuin ok2: lesser resolution and imaging quality than OK1, otherwise it's tonally similar.

Head-Direct RE0: light bass, poorly extended but clean. Flawed, distant and lifeless midrange. Awesome treble quality, extension, resolution and overall sense of smoothness. Small soundstage for IEM standards.

Head-direct RE1: fuller sound, deeper bass, chesty midrange. Treble is almost non existent and fails to add excitement.

Shure E500: plasticky mids, full sound with strong bass, some lower treble sharpness, but rolled off upper treble. Decent soundstage for a iem.

Triple.fi 10 pro: awfully uncomfortable, stiff cable. Detacheable cable is a pain since there is the risk to lose the earpieces. Bass is perceived as big, there is decent depth. Midrange is pretty clear with foamies, treble is peaky and can be sibilant, especially with the wrong sources. Sort of U shaped frequency response. Big soundstage width and depth.

Super.fi 5 pro: same conveniency issues. Soundwise, it's bassier than the Triple.fi and the treble spike is much sharper.

Etymotic ER4P: digital sounding. Low bass volume, although deep. Intimate midrange. Treble is very peaky and sharp, sibilant, analytical, hyperdetailed and sickening. Puts out lots of unneeded details that are meant to stay in the background.

Etymotic ER4S: bass is more annihilated. Fake details are raised and you'll be able to hear dry lips of the singer moving when he's harmfully close to the mic.

Yamaha HP-3: orthodynamic, must be damped. Bass and treble are easily tuneable and reach deep frequencies. Midrange between 1 and 2 kHz is very recessed and basically unfixable, making for sleepy vocals.