That's actually a very good questions. I'm not sure. I "think" technically. But "every other way" was probably a bit of an exaggeration.
In saying that, I mean that based on my understanding of sound they seem more realistic and presented correctly. Whether everyone agrees I can't say. However, to me they are more believably "real". The presentation allows you to hear separation better, that is technical as far as I would think. I simply don't hear the level of separation and details in that regard with my er4s. Frequencies being equal or not, I notice more distinction in things that the er4s doesn't show. A guitar playing with an orchestra stands out as being in a real room and easy to hear, no matter the frequencies. The er4s (comparatively) sounds more like the guitar is "mixed in" with the other music making it hard to focus on the guitar's finer details on it's own, again relatively speaking.
Stereo width is wider. I don't know what is technically "correct" with width, but the wider width sounds better to me, because again it allows instruments to stand on their own more believably with space between them.
The frequencies are smoother and easier to listen to, again signatures being equal (with eq) or not, they are simply not as fatiguing for lack of better words. They don't require as deep insertion, even when putting them in deeper than they are probably designed for. That is at least a little more comfort, technically. However, I do know that the etys can be comfortable as well, but not "as" comfortable.
They sound like they preset more depth. Again, frequency response doesn't seem to matter. I hear "into" the room and almost "past" the instruments if you try. Things sound more believably real in that sense, as though the instruments are really in a room that you are really listening to. That's a lot of reallys.
I think stock, the er4s is technically better frequency response, even with the perfect f111 fit. They also boast better isolation and probably durability. They sound amazing and I'm not getting rid of mine probably ever. And I'm also probably not buying the f111. If they were the same price and fit wasn't an issue I'd have a pair yesterday.
So, perhaps I spoke a little to literally, but I think most people that hear them will agree they improve upon most areas of the er4s, while being warmer with a normal fit. The lacking treble is pretty much perfected with the perfect fit, however, this is very hard to consistently achieve. So, whatever you make of that.
Otherwise, technically, they seem very similar with distortion being non-existent audibly. However, the f111 is more prone to noise from the sensitivity. However, that is based on the amp. I have one amp that is silent with them and my fuze has a low noise floor with them. They are both really smooth with the frequency responses they have. No spikes detectable. The sensitivity gives the f111 an advantage for portable use while not really sacrificing anything with a good amp...
