I'm probably making a big mistake, but I will give some very very very fresh impressions of the er4sr reference model.
I haven't got to the sx yet. And these impressions are almost guaranteed to change over time or at least develop and mold into a final opinion of some sort.
I'll start by honestly saying I believe the original er4s is the best earphone/headphone I've ever heard, period. I believe it to be closer to a pair of studio monitor speakers (if not better when acoustics are poor) than anything i've heard. With that said, nothing is perfect, but the er4s is perfect "enough" that I get the most unbelievable enjoyment out of them and ALWAYS go to them over every other headphone,... And i've tried a lot of them.
I have the shure 940 and had the hd600 for a while, and while they are excellent headphones, and many prefer "full size" headphones for bass tactility, I would take the er4s over all of them with no questions asked.
If it weren't for convenience, comfort sometimes, and having access to various signatures for comparing while mixing and mastering music, I'd probably feel confident enough to only own the er4s and nothing else.
Preamble aside, how do the new er4sr sound?
I'm not sure yet.
First and foremost, if you like the er4s you will like the er4sr. They are clearly (pun intended) an etymotic earphone, and clearly the best earphone on the planet just with a preliminary listen. But they are different.
In fact, a bit more different than I expected, but not in the way I expected. I had assumed the response was either going to be identical, or they were going to have a slightly different treble or bass "flatness" in terms of equilization.
But I have a very strong feeling people who like red filters are going to LOVE these. They don't sound like a red filter er4s per se, but I truly get the impression the 3k honkiness is completely gone. Not that it sounds that different from the er4s, but somehow they are more relaxing. I'd almost describe them as more V shaped, but it doesn't really seem like a frequency response thing. They are just more laid back.
Now, relatively speaking, remember we are comparing an er4s to an er4sr. These are much more alike than they are different. But holy poop. I'm listening to driftwood by dan gibson (search for it) and it almost brings tears to my eyes.
This slightly more relaxing sound almost gives the impression of a better bass response. But it is a similar effect to the red filters doing that. I'd almost say the mids in the new model sound a bit more relaxed, which make the treble sound a bit more present. The treble seems a bit drier. Everything seems slightly drier. Like what the er4s had in smoothness and silkiness these have in a dry spaciousness. I'd almost say some people will probably find them a touch more spacious due to this relaxing aspect.
Certain details are definitely a bit more apparent. Like guitars with grunge seem more grungy. Sounds in the background sound more apparent. It's almost like the er4s if someone moved the sound a bit further away from you - less in your face. But not distant in a reverbated sense. If anything the opposite. They sound further away but drier. Again, a slight difference, but I really feel this is a real different and not just imaginary.
And lastly for now, I feel the instrument separation is clearer. I feel various instruments in a mix are easier to distinctly hear.
Let me listen more and do more a/b and get back to you.