I'm suffering from information overload, I have read this thread twice (its that good).
Bila, what are the dimensions of the cups you display in part 4 of your video? That looks like something I would want to recreate while finding a way to fix the non-liberated drivers into the wood cup. I am going to take a shot at some point making a pair of those cups. I have a friend whose father is a woodworker and I should be able to figure it out considering I can work metal on a lathe and mill fairly well.
Wow. I envy you your skills. There are many here on HeadFi who would be thrilled to buy aluminum cups since aluminum has such a high velocity of sound. With respect to the dimensions of the shells, I have two rings, one serving as a first stage, forward chamber and a second stage, rear chamber. The first stage "inner" has a hole of 1 7/8" with an outer dimension of 2" while the second stage "rear chamber" requires a 2" drill saw and another at 2 3/8". These do not create an exact fit. They're sized up a little, which is to say they still leave some room. Where things fit loose, I usually shim, set and glue.