Regarding the sr vs. xr response. I can say firsthand that my two pairs personally sound identical in the mid/treble. They may not even measure identically, but the overall upper response is pretty much indistinguishable. I haven't done excruciating listening tests, but I've listened to both on their own for a while now, and I'm very very familiar with the er4s.
So I can say that to my ears, the new models both sound the same other than the bass boost. I find that the boost isn't enough to really "mask" anything. I would venture as far as to say there is no masking of details. If you can hear something on the sr you can hear it on the xr. The difference is in the "perceived" masking.
In other words, while technically any boost in one frequency area will "mask" others, the masking usually comes in the form of distraction. This is exactly why there is "mixing" when recording an album. If one sound is too loud it drowns out another. This goes for "instruments" as well as "frequencies". But that doesn't necessarily mean you can't "hear" certain details, but attention is drawn away from them.
So if you think of it in this way, the best way I can describe the xr bass boost is that it draws your attention just a little more to the low end of the spectrum and a little less from the treble transients.
Listening to a song with guitars and basses, the sr might draw your attention to the texture of the guitars. The xr might draw your attention to the bass guitar more. If you listen to the guitar though you would still hear the texture, it's just that the balance is lsightly shifted to the low end.
Let me be clear though, the difference between the two is much less than the difference between more earphones. So one might argue that there is almost no masking and it is just a little more bass. But I guess that might depend on how you focus your attentinon while listening. I feel personally that I "notice" certain instruemtns or sounds more on each, but I never feel that either has any "hidden" details at all. They are both sufficiently accurate and smooth in reponse that all details can easily be heard with both.
In fact the bass boost is such a smooth and gradual curve that it really helps eliminate masking effects that you would typically expect and more just sounds like a slight "tilt" in the response. In other words, it isn't a bass peak or bump as much as a gradual curve bringing the whole sound a bit more "meat" or body.
I agree completely about the people who found the er4s bass thin. If they didn't think it was awful, and just thought is needed "a bit more bass". The xr will probably rock! If you found the er4s was almost perfect, the sr is even better in bass perception, but don't take that to mean it has more bass... It's just that the bass sounds better to my ear. I will always say the er4 of any model should have a bit more sub bass, but that's just aiming for real bass perfection. The sub bass is superb, but the lowest end of the bass is the only thing i ever feel could be improved by a few db.
I'm just blabbing now, so i'll stop. But both models are superb, and if you thought the er4s needed a bit more bass, the xr shouldn't sacrifice anything at all from the sr for you.
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