For the most part, it is simply a matter of looks.
Bamboo is lighter and stiffer than the MDF usually used to build the cabinets. Some would say this is a superior material for speaker cabinet construction. I don't know if I'd go that far. It is certainly a good material, but I can't say is I've heard any significant improvement in sound quality when working with bamboo. To me, it is a matter of being a more "green" material and perhaps aesthetics play a role in it as well (if you like the looks of the bamboo).
As for the black finish, most people looking for black speakers are using them, at least in part, for home theater. So they do not want them glossy. Satin is a nice alternative. Satin finish is also what you normally find on most high-end furniture. It makes wood look more natural compared to gloss which can look nice, but perhaps a bit plastic.
When we do black, we can do it with a flat surface (which we normally do) or we can do it over oak, ash, etc. and leave the grain open. Some people like seeing grain in the surface and we certainly don't mind. You need far less finish if you are not filling the grain. So having grain show is the easiest way to finish black speakers.
I hope this answers your questions.
- Jim
