very funny how people who replied this question doesnt seem to have personally listen to esw9.
its a unique headphone by itself, so far i've yet to find anything similar.
closest to its sound would be ath w10vtg, which is also similar to ad300. its closed, very balanced (means doesnt emphasize a certain frequency) and its colored in a very nice way, tonally there's a touch of sound in the tone, but it also specific to each tone and helps to amplify difference between the same strings, say, difference between violin a and violin b of different make. this is something you will not find in any other non wood headgear, the wood coloration. it also has audio technica's voicing signature, which is different than all sennheisers, all akgs, all beyers, and all shures.
based on how i remember esw9 compared to my ex ath w10vtg, i can give you the following opinion, since i have auditioned the um3x as well.
Imo esw9 can be considered a top level portable headphone, it can take the fight to ath woodies, hd650, akg k701, etc.
it's easily above ad700 in terms of smoothness, delicacy and presentation, something you'd get from any top level headphones.
um3x is totally different.
the main thing you should know is that esw9 is mid centric, vocalist, pianos will be the main presentation, bass and treble are supporting behind. um3x is bassy and less vocal than ews9, more u-shaped. bass will be more in focus, vocals will be pushed further behind the overall presentation, treble, might be similar, but i'd say u will hear more details um3x, from bass to treble, even the mids, compared to esw9, but the presentation will not be as thick on the mids. u get more details, more clarity, but u lose some body and weight, the hefty sound coming from big driver.
as for relaxed sounding, i can say both are relaxed sounding. both is not offensive sounding. both is up there in terms of smoothness and delicacy, ur ears will tell u which one is better in that regard.
however bass and details is more focused in um3x, meaning is focused or lumped together. this is a limitation of iem to a headphone driver which have more room to breath. u wont have the relaxed sounding that headphone can give because of 'the scale' of the presentation. headphone can give bigger scale, just like comparing speaker and headphone, speaker can give bigger scale.
what iem does better than headphone is the focus in sound. sound is immediately injected to ur eardrums. u get more focus, but lesser scale. hence, u can hear more details, more micro details. isolation helps you hear better as well. if this is what you are looking for, then its probably a right option.
but if ur looking for the same sound in compact size, i've yet to hear an alternative to esw9.
but your description seems accurate. Yes he won't find the soundstage on the IEMs, but he will find the detail and superb isolation he's looking for
