I have the older er4-s series with the red and blue earphones. I'm using the HUGE yellow foamies that isolate like 46db with a deep insertion. The deep insertion can hurt at certain points. But I get used to it. I will get my amps in friday, which will definitely change my listening experience on the er4-s's. I have to turn my volume on my ipod up to 65% to be at a soft volume comfortable listening level, they are super accurate, the punch and impact is there, but they are kind of weak because the er4-s is really meant to have an amplifier.
EDIT: Can anyone comment on etymotic's customer service? Are they friendly?
Maybe you should use the tri-flanges (LOL). Anyway it's not because they need an amp that's why the punch and impact is weak. The ER-4P doesn't need an amp but it is weak as well. I guess the ER-4 are meant to take accuracy over bass and impact. So that's the sound signature of them. But then again, I think the HF5's impact is stronger.