Appreciate the response. Personally, I didn't mind the slight discomfort from the grados. The hd650s are definitely easier to wear for extended listening, but pretty damn big.
I actually sold my 225i for the hd650s, which I do not regret at all. To me, the 225i was a bit too harsh at louder volume for my preference. The hd650s are very smooth and generally warm sounding. I've read that the ps500's aren't as bright as any of the models below it in rank.
I guess I'm just starting to get that itch again.
Grado refers to the PS500, as having a "hybrid air chamber", and the HF2s were also produced with this. I believe they are referring to the mahogany interior, and aluminum exterior, of the shell for the drivers. That is where the superior bass response comes from, in my humble opinion.
I auditioned the 325is a while back, and was totally dissatisfied with the listening experience, because it was totally lacking in the bass I tend to crave...