I did some comparative listening to Miles Davis' Kind of Blue on the Etymotic ER-4S and the Grado SR60. The Etymotic ER-4S was connected to a Total AirHead headphone amplifier (with crossfeed off, powered by a regulated AC/DC adapter at 4.5 V), which was connected to the lineout of a SlimX...

I finally am able to get a pair of Etymotic ER-4S. I feel happy. There's one thing that makes me curious though: How do I tell if my Ety is actually the ER-4S, not ER-4P or ER-4B? There doesn't seem to be any marking on the phones or the wire. There are two serial numbers, one on each...