Ive mentioned this before. I put my rs1 drivers in my hf2 shells and didnt get the same amount of thump that the hf2 driver in the hf2 shell could produce. And the same with putting the hf2 driver in the rs1 shell. The hf2 driver is different in someway.
OK, so there's proof (driver stampings, etc.) that Grado apparently utilizes the same drivers for their SR series of headphones. However, my SR325i headphones have quite a distinct difference in sound to them. The highs are more tamed and there's a better lower end. With that being said, I'm assuming all this can be attributed to the aluminum cups that the SR325i utilizes?