Seems I need to investigate the Etys then... Etymotic provided my first introduction to 'proper' iems probably over a decade ago now. Can't remember the exact model, but I do remember being disappointed by them given the reception they were being given in the press at the time, & I wasn't enamoured of the ear-raping insertion depth required to get a good seal (though snipping off the 3rd flange helped). As it turned out they weren't too well made either so didn't last long. T'was a long time ago though, so perhaps they've improved things. Worth a try.
The UE600vi are currently super cheap here at the moment - largely due, it would seem, to the exceptionally high number of reports of the cable failing at the jack - a great shame since their sonic capabilities appear to be universally applauded.
Many thanks for your input Joker - the resource you provide with The Headphone List is astounding, & that you're willing to field such a huge variety of individual questions even more so.