That's exactly what I was saying, though I'm not sure if you're trying to refute anything I said. Flat response is indeed a BS form of marketing for high-end audio equipment. People who buy low end like to hear that it is "a lot of base!"--ugh.

But, as I mentioned, flat response is essential for mixing and mastering. For very well mastered music that's not made for the radio or extremely wide consumption, relatively flat response is very nice to have--but it's by no means close to the balance of a great set of studio monitors, which aren't geared for listening to music for enjoyment but are great for analyzing what's actually there.

I own the ER-4P's and they're very good. Of all the earphones out there (in-ear and regular earbuds) they are at the topic for balanced response. To get the best out of these, as with any high-end ear/headphones, you should listen to them through an amp. The ER4-P's need a small adapter that changes the impedance, or ohms, to make them match the amp--the ER-4S are made for an amp without that tiny adapter, but don't work as well with a self-amped device like an iPod.

I would not go for the 4B or anything made for binaural recordings, unless you already have a collection of binaural recordings that's amongst your favourite music. Very little is recorded for binaural reproduction, it's more expensive and it's harder to come by. Canalphones like the ER-4P's already reproduce a stereo soundstage incredibly well and create a mild effect that you're listening to a binaural recording from having the sound aimed so directly into your ear. Soundstage can be described as the virtual space that's created by a recording with more than one channel (stereo=2). Good soundstage has to do with how cohesive, convincing and accurate the virtual space is. Stereo fields can appear too "far apart" or "close together," and this is bad soundstage--almost entirely from the speakers or headphones as opposed to the amp. The ER4-P's have excellent soundstage, noteably for solo instruments. Simply amazing with a solo cello or guitar.

I can't believe I referred to wiki, but it does tend to have good and concise descriptions of things that are tricky to describe, like soundstage:

"According to audiophiles, the quality of the playback is very much dependent on how one is able to pick out different instruments, voices, vocal parts, etc. exactly where they are located on an imaginary 2D or 3D field. This can enhance not only the listener's involvement in the recording but also their overall perception of the stage."

Anyway, I went off track. But the biggest reason to not spend money on binaural earphones is that they are not made for regular recordings, ie. 99.99% of what's out there. Unless you have tons of cash and want to throw down a few hundred to try out something new (which you can do just as well with regular headphones), go with earphones made for regular recordings. Binaural recordings already sound very convincing on regular earphones, especially accurate ones like the ER-4P's, so any improvement from the ER-4B's is highly unnecessary unless you're a big binaural recording afficionado with cash to spare.

Also, binaural recording is very interesting and worth a listen, but it'll never replace your regular listening or the music you already like. At most, it'll expand what you listen to by 5% or so and give you a new kind of listening experience, which is very neat but hard to justify a big expenditure over.

Google "binaural recording" or something and give some of the free samples out there a listen with whatever set of headphones you have lying around. Find some music suitable for binaural recording (big bands/anything electronic or amplified = not very suitable, but solo instrument = wow) and close your eyes. It's fun.