James, That's actually a good question. Actually, I believe the aluminum cups may tend to make the bass sound a bit more "metallic" versus "natural" like it would sound with music as in a musical instrument. I do often swap between my stock SR-325i Grados and my "woody" modified SR-225 headphones. They do have different sound characters. I like the SR-325i for various reasons. However, I love the SR-225 for many other reasons for how it tends to treat the music. However, the SR-225 headphones have more mods - opened holes, felt installed, Dynamat, etc., so it's kind of hard to really say that my comparisons can be truly an aluminum vs. wood comparison. However, I am awaiting wooden "liners" from Bilavideo for my SR-325i headphones that I intend to install. This will allow me to keep the classy look of my Grado "Goldies" but offer some of the tone benefits of wood with the liners - or, at least that's my hope.
Oh, and don't take my comments that I make regarding color choices too seriously. During my daily routine, I work in a very "politically correct" environment and I find it hard at times because one can't really joke a little bit without it possibly offending someone. However, here on the forums, when the opportunity exists to make such a comment, I'll step up and take it. Though I never mean it in such a bad way or to hurt anyone's feelings. I'm just glad that forums exist for us to "vent" a little bit from all the political correctness that many of us live within during our daily lives.