i could just make the door-wall using 6 inch studs and then do a
double-door thing, with the inner part between the doors getting
stuffed up with sonex and stuff like that so the perimiters of the
doors have about a 4 inch thick foam barrier all around.

then juice up the insides of each door with a layer of sheetrock and a
layer of that auralex sound-block vinyl stuff.
although a single "star trek" door would be more elegant.