Yup, ms2i cups indeed.
I had the aluminum inners too, but I think you knew that.. and I agree, the inner chambers matter more.
I would imagine that the glue that holds the inners and outers together would matter more than the outers. I know Rhydon uses some insane anaerobic glue that is supposedly harder to break than the metal in the gimbals (I wanted to remove the tips and change the rodblocks). I would imagine that Grado's hot glue likely has some interaction between the plastic inner and metal, plastic, or wood outer. I would bet that the effects/resonance of the wood effects the inner, which would effect the sound more than the outers.
I'm pretty sure Rhydon doesn't use glue at all. I think he pressure fits them somehow. I've never quite understood the process, but from what I understand, they'd be mighty hard to get apart.. Maybe I'm wrong though, it's been a while.
FWIW, I used a piece of electrical tape on the inner to make the outer shell secure on my aluminum magnums.
You may be right. My magnums looked so nice, I couldn't bare to tinker too much, then I listened and the desire to tinker entirely faded. We all know for sure though, that Grado uses hot glue.