Another followup. I got my sleeves from ACS about two weeks ago. Total turnaround time was right around a month from when I had the impressions made. (That's excluding the additional month I was waiting for DST-Swiss -- who is no longer in the picture.) I paid out-of-pocket for my original impressions which DST-Swiss still has hostage; ACS comp'd me the fitting and sleeves for the replacements.
I've been using them a lot and the long-term comfort is great. I can easily have them in all day without any problems. Using the narrowest of the flange inserts that came with the Etymotic HF2, I could only wear them for an hour or two. For me, the improved comfort is the real win.
Isolation seemed at first worse with the ACS sleeves. However, I lose the seal pretty quick on the original Ety sleeves, so in reality unless I keep pressing them back into my ears, the isolation on the ACS sleeves is better. Any jaw motion (say, walking and eating) would wiggle the Ety sleeves out, but the ACS ones stay in much longer. They also take less work to put them in and out in the first place. I could imagine that the ACS seal could be improved if they were made out of something else -- say, covered in a thin microlayer of memory foam, or something like that. The flanges on the Ety sleeves are softer and more flexible (because they're thinner) than the thick silicone that the ACS parts are made of, so naturally they reach a perfect seal a bit better.
The ACS sleeves definitely feel 'bigger' in the ear -- they touch a lot more skin. I loved the tiny-ness of the original Ety inserts, since they were so light and touched almost nothing.
Sound quality is about the same on each. I thought at first that the ACS were a bit less rich than the Ety ones, but after listening more I'm not so sure about that. The earphone body definitely sticks out of my ear further with the ACS sleeves -- a good couple of mm further out, really. This is just because the sleeves are a lot bigger. The sleeves aren't quite symmetrical R/L -- one's a mm or two longer -- but they both put the speakers the same distance from the ear, which I assume is the important part. They certainly sound balanced.
One unexpected negative: the Ety HF2 have a microphone for use on my iPhone. When talking, I hear myself a lot louder with the ACS inserts, than the Etys. Must be just that thick silicone connects to the bone much better than the thin flanges of the original do.
Summary: no-brainer for $100. They're super comfortable, stay in place well, and sound essentially as good as the original Ety inserts. Thanks to Matt at ACS, and Rick at Ety, who quickly handled the problems I had with my original order through DST-Swiss.
Edited by Hankk - 3/3/11 at 2:05pm