There's a few things that I've found over time if it helps.
Seal isn't everything. It is absolutely critical, but there are other factors just as critical, at least in my experience. For instance, I need to pull my lobe up, open my jaw a bit and rotate the tips as I insert them as though I'm screwing them into my ears. I need to do this in a very exaggerated way so that the rotating prevents ANY buildup of positive OR negative ear pressure. If I just push them in I get pressure pushing into the ear. If I pull on my lobe and open my jaw, sometimes the tip will go in, but air will get pulled into the flanges and when I let go it creates a slight vacuum effect with pressure sucking my ear a bit. In either of these cases, I might hear bass, but the overall frequency curve is off and things sound hollow or harsh.
By rotating them a lot while inserting them the air pressure stays equalized and the sound is correct. However, they also need to be very deep. Etymotic said they usually sound better as you get deeper. This is very true in my case. Even with the triple flanges fully inserted to the depth most people have photos of, I don't get the full low end response. When I push them in very deeply, to the point that the cord is against my ear, the bass response is more and flat with the treble. In fact, it compares almost equally with my pfe112 which should have 6db or so more low bass. This is why I think a lot of measurements and people think they lack bass. They aren't bassy, but they are very neutral bass, when and only when you have them very deep and "properly" sealed.
Beyond that, they definitely will sound harsh to some people that are used to bassy or mid heavy phones. Ironically, a lot of supposedly "high end" earphones are very lacking in real high treble and are bassier and more mid centric than a true neutral response. So for a lot of people the er4s will sound very treble centric. However, when you achieve the proper sound they are very flat. So, I suggest everyone listen to them for a while without comparing anything and start at low volumes and move up as you are comfortable. They are so revealing you don't need them as loud as other phones sometimes get played.
As for the er4p. From my listening experience they are basically an er4s with rolled of treble. This might give the impression that the mid/treble is boosted, but I think it is more that the high treble is lacking. They sounded identical otherwise to me. This makes sense, because all the 75ohm adapter does is change the response curve to have a flat treble area instead of rolled off. I still found the er4p to be superior to a lot of earphones, but I could never take them over the er4s personally. I want studio monitor sound that is reference quality, and the er4s is exactly that for me.
Lastly, some people simply don't like studio reference "flat" sound. There's nothing wrong with that. It doesn't mean your earphone are bad or the etys are bad. Some people like to have more bass or more treble or more mids or any combination of traits. That's fine. You may just want a different set. But with any earphone, I'd give them a good amount of time. Most earphone companies will tell you to break in the tips for a week, because even that affects the sounds. As the silicon gets softer they mold easier to your ear shape. Just some ideas...
