here's my impressions on the bunch (and also compared to my MK2 rev1). mind you i haven't had the opportunity to listen to the MK1 rev2.
the MK series have similar sound and soundstage one another, but with the MK1 focus on bass/midbass, MK2 on treble (also have the most snap/attack on the sound), and the MK3 on mids and most balanced between the MKs. no significant difference in soundstage between the balanced and my rev1 single ended.
all off rev2 have reduced bass volume compared to the rev1. that might explain that MK2 is the most popular among rev1, and MK1 among rev2.
the 300 ohm has the most mid emphasis on all willsounds, also the most rolled off bass and slight roll off treble.
notes: all of the MKs and 300ohm are using thin monk-like foams, and have balanced jacks (except my MK2 rev1).
the PK32 has a thicker mids compared to the MKs (around 500 hz bump). this result in more intimate sound and seemingly smaller width in soundstage, but also have more depth compared to the MKs. overall sound became more analog/tubey. treble is softer than the MKs, but not by any means dull. Bass is plenty deep, surprising for a yuin shell, and can compete with the MKs.
notes: The PK32 is using full hiegi foams. i don't like the thin foams on it (too dispersed sound). i also don't like donuts on it (loses airyness and makes the soundstage closed in)
notes:all the rev2, 300ohm and PK32 have a more rubbery and more pliable cable compared to the more plasticky and harder rev1 cable.