I don't think that there is anywhere in the UK where you could demo a reasonable subset of Ratfarm's shortlist. If there is, it's in London and a pain to get to for half the population.
Maybe there are a handful of places in the US where you could demo these - but my bet is you're talking about one in NY, a couple in California and maybe one or two somewhere else. For most people this will mean thousands of miles of travel. Most Japanese who might want high end IEMs probably do live in reasonable reach of Akihabara, but the US is BIG.
(But even in Akihabara I'd be surprised to find SM64s, which would reasonably seem to be top of the list, for demo - Ear Sonics don't seem to be into conventional retail.)