Updating 4 years later. Someone recommended changing pads and they were right! It was the F Pads that saved the Grado line for me. Grado SR80x, SR225x, SR325x, all with F Pads and could not be happier. Like I said 4 years ago, I am not a basshead, but changing the pads not only revealed the capabilities of the Grado cans, also got rid of the shrillness that bothered me so much.
So no need to go above the 325x. Just made sure everything I got from Grado had the F Pads.