Psyche... sort of, but not exactly... at least, not to my ears.
Grado (to my ears) sound is very up front, aggressive, fun. That sonic character is expressed differently in different Grado phones. I owned the 125s for a while (2 years or so) and enjoyed them a great deal, especially when paired with a nice tube amp. Have listened to and enjoyed a wide variety of Grado cans. Singlepower amps or Carlo modded Melos + upper end Grado = very, very nice combo to my ears for rock, metal, progressive, jazz.
However, the difference for me between those and the Etys is quite noticeable. The ER4 are clean and detailed... everything that's in the recording comes out (good and bad). I'd describe the sound as neutral... meaning that you get less noticeable color or character from the headphone itself compared to the Grado sound. That difference isn't good or bad in and of itself, it's just different. One may sound better to you than the other.
While the general character of Grado is generally described as being up front, the way I would describe the Ety sound is pure detail (from the ER4s anyway... I didn't like the sound from the regular ER6...). If you are a detail freak, you'll probably enjoy the Ety sound.
BTW: the difference between the ER4P and S is simply impedance. The S version has an additional 75 ohms added to it. The cables are the same, the drivers are the same, just the ohms are different. And, remarkably, the sonic character is different! To me, it seems as if the entire sonic spectrum gets shifted slightly and extended... the P have a bit more mid-bass and the highs have slightly less sparkle and extension. Add the addition impedance (and drive them appropriately) and the sonic spectrum opens up just a bit wider. It's a remarkable thing to experience...plug an adapter into your ER4P and suddenly the sound changes... to my ears, for the better. That difference is one of the reasons that I went for the ER4P again. Can easily buy an adapter for $25 - $50 (or make one yourself for even less!) that in essence gives you another set of terrific headphones for a very modest price.
Good luck!!!
BTW: Just got notice that road dog accepted my bid ($130) for the M5s.
Bruce