Roy_jones, you have discovered a few things that I found, and a few things that I've been growing tired of over the past few months.
To me, your descriptions seem spot on. Objectively, the e4 reproduces sound that is more resolved and more accurate than the um2. You seem to be the only other person who has noticed the (rather obvious, imo) vocal coloration. My guess is that the bass driver plays more of the spectrum that it's intended to, giving a fuller, darker sound to the music. I didn't know the 627 is regarded as a bassy opamp. My class-A ne5534 has much more bass and less clarity in the treble than the 627, so I'm surprised to hear that.
With the um2's, the tips do make a big difference. If you are using the tri/bi-flanges, they are the most trebly of the various tips, I found. The biggest advantage of the um2's is their ergonomics and fit, I think they are the best of any IEM I've tried. For me, though, the e4's are more comfortable than most iems.
Another thing you now see is the inaccuracy and unreliability of much of the information being spread around here at head-fi. It's a fantastic site, and much better than most on the internet in this regard, but people are still unable to separate their subjectivity from objective differences. Rationalization is certainly the most frequently used eq.
It also seems people care more about what sounds pleasant than about fidelity, which I thought was the point of this site. It wouldn't be a problem, but it's that people claim their euphonic preferences as objective fact, which is pretty annoying. I mean, I certainly don't think I know what I'm talking about, but I am aware of when I am stating what I believe is fact and when I am giving an opinion.
Either things have gone downhill in the short year I have been here, or, as I've learned more about headphones, and as my ears have been trained to hi-fi sound, I am better able to see that there is a relatively small portion of people on here that really know what they're talking about. In the end, you can't stress about it too much, because things aren't really going to change. Just state your piece and move on. If someone doesn't like what you say, they are most likely going to reply saying you're wrong, so that people reading don't actually know what the truth is unless they have experienced it firsthand.
To me, it is a fact that the e4c will never sound like the um2, and the um2 will never sound like the e4. Regardless of eq'ing. The um2's treble is more recessed than the e4, and it is also not as resolving. If you eq the treble up more, it helps, but it still doesn't reach the right amount of detail and balance with the rest of the spectrum. Then you exceed the capability of the drivers and the treble becomes harsh and sibilant. The bass of the e4 can only be upped so much before it starts sounding bloated and...bad.
I also agree about the limited usefulness of extensive eq'ing to make an IEM sound better. In the portable situation, almost no one has that kind of eq. And I feel it's sort of pointless at home, since $100 full-sized headphones sound better than most iem's.
I agree that the er4 has greater clarity and better accuracy than the e4. However, I think the er4's are a bit harsh and sterile, to a point where I did not find the music enjoyable. So, even though I believe the er4 to be a technically superior canalphone, it's not by that much, and I think the e4 is the be compromise between an accurate and detailed sound, while retaining some warmth and pleasantness to the sound, without being harsh. But that is just my opinion.
