ER4S is smooth and extended with the proper insertion, it's treble is based on the human-related-transfer of perceived flatness and has some conservation in the most sensible areas of the ear (6-9k). PFE with gray filters and stock tips are too hot,the stock grey silicones are horrible for them. PFEs need tips with a small bore to resonate that higher treble (I use Klipsch oval tips), once you achieve that they're not offensive at all and very flat. EQ5 are more offensive than both and you cant use small bore tips because it's acoustics makes it resonate part of the mids as well. Still, it isn't that bad. Those that have the issue, try longer tips, biflange or triflange.
I don't really understand the resonate part. I think it's just amplitde and band emphasis adjustments due to mechanical resistance. There's not a large enough acoustical environment to create mid resonances but if your just using it as a sonic que, I get it. I agree that the grey filters are a bit hot on the PFE but like you I still find them preferable to the blacks that mask too much. I do like the sound better with their own tips than others I've tried. Not saying that you're wrong about the ovals and it's just our opinions anyway but I don't find the stock tips horrible by any means, just a bit too present. I need to get some klipsch ovals. Seems they get a lot of use by those that own them.
I liked hybrids on the E-q5 to tame it a bit. It did bring th mids and bass forward by knocking down the top a bit but real hybrids don't sound ringy or resonant when doing it, for me.
Edited by goodvibes - 6/20/12 at 3:35am