Spendy and Splendid ...
That is what I took from an iChat AV conversation with someone who has real golden ears - the sort that get used in a certain well known symphony, music conservatory and ultra-high end recording firm.
I have never tried these and am unlikely to as they are way to expensive for my purposes and ears - I do promise a thorough review if someone wants to give me a set though...
From my notes. You visit an audiologist to have impressions made of your ear canals. These and a check for about $550 go to Ultimate Ears for a set of EU5C earphones.
He notes fit is great (it should be) .. he has been using Etymotic Research ER-4S earphones with a small class A preamp (!) on his home system. He uses ER-4Ps on his iPod (interestingly enough this guy is very happy with AAC compression at 192 kbps).
The claim is these "aren't that much more expensive than ER-4Ss once you have custom impressions made and the sound quality is a bit better..."
I guess you pay your money and take your pick. I am completely happy with my much less expensive Etymptic ER-6 transducers. I suspect I would not be able to detect a sonic difference between them and EU5Cs.