The 225's have an edgy, solid sound that complements rock music very well. My Godflesh CD's sound their best with these cans. The 325's have a more accurate sound, and many people say it is brighter, though I haven't heard them myself. I find the 225's to be o.k. with jazz and classical, though not great. For rock, the 225's can't be beat (except maybe by the Beyer 250-80's). For electronica, though, I would consider getting the Sony MDR-V6's. The bass on the V6's goes deeper, and I think is more suitable for electronic music. Why not get both, since you have enough to buy the 325's outright, and have a very versitale set of cans?
P.S. In my opinion, the V6's sound just as good directly from a portable as from a pocket amp, so you could keep the Airhead at home with the 225's and take the V6's on the road. The V6's are my current choice for rock on the go without an amp, that's part of the reason I'm selling my 225's. They sound good directly from a portable, but sound lots better with an amp, and the Grado/portable amp combo is just too bulky for exercise, my main use for portable listening.