Thanks for the comments, guys.
@Miney: The subs are bamboo with a bit of a reddish tint to it and a sturdy finish. My pictures don't do justice - they are beautiful. Jim had advised to go with veneer - which would've looked the same and saved a few dollars - but in the end I went with bamboo plywood instead. They weigh 160 lbs each; MDF (with veneer) would've been probably more like 250. Jim had forgot to take pictures before I picked them up; I sent him some that if he can clean up well enough, maybe he will end up putting one on his website.
I did see some veneered speakers while I was at his shop that were really amazing. It was pretty cool to see them partway through the process and not fully assembled; not sure how they get the veneer onto extreme curves, but they do.