Hey, just wanted to say thanks for this thread. It has helped me a lot.

The second grommet does not replace the Jack [J5]. It is in addition to it. When you cut the holes in the Altoids tin. The hole is bigger then the knobs and jacks.  With the Potentiometers there are knobs that cover up the holes (yes the pots are on the out side). With the  input and output...

I have made 3 of these and they do sound good.     In regards to the materials and alternatives, my suggestion is that you get everything from mouser (nothing against Digi).  It is just that the only thing that you need from Digi is the volume knobs. Mouser has plastic ones that will fit...