16x16x16 is 4096 elements, which is quite a bit to try to do in "real" 3d. But, you don't really have to, since you can optimize for your cube model. If you don't need to rotate the cube or move the camera, then you can just precompute the screen positions for each element. You could even use pv3d for this purpose. If you do need to rotate the cube, you'd probably be better off using the new flash10 2.5d transform features.

I'd agree with neznein9 that you're probably going to want to fake as much 3d as you can get away with.