I should listen to my other gear more often.
1: Sansui SS-100: Smooth as butter. Lacks a large low end; needs new pads. Fantastic soundstage and clarity. Treble is perfect. Doesn't like being driven loudly. Uncomfortable as sin.
2: Pioneer Monitor 10-II (extensive modifications): Barely below the Sansuis. More bass. Equal clarity. More 3D in presentation while being smaller in overall soundstage; hard to describe the exact differences, more of a preference thing. "Harder" sounding treble (distortion? ear-side ringing caused by earpads? dunno.) Upper midrange hole. 1kHz peak. Isolates like crazy. Much more comfortable.
3: Etymotic ER-4S: Sending this one back, but not because of sound. Love how these sound. Just a bit too dark compared to the Sansui. No, I'm sending these back because I am physically incapable of wearing them. Several painful zits formed in both ears after about a week of use at work. Guess I'm really not an IEM guy.
4: Pioneer SE-500 (modified): eeehh. Very little bass and lower mids, and no warmth at all. Smooth and clear as hell but that's still not a good combination, and it can sound fatiguing because of this. Maybe the right pads would work.
5: Beyer DT48 S 5 ohm: These are something I like, that I really shouldn't. Literally no bass at all and less treble/upper mids than the SE-500 above, but there's something "special" about the presentation... they are definitely unique and do see use occasionally.