How do I replicate the taste of prepopped movie theater popcorn?
There's a different variety of popcorn used for pre-made popcorn, as it comes out more spherical and thus less prone to breakage once it dries out.  I've always seen it called 'mushroom popcorn'.

I've never made it specifically, so I don't know if the flavor is something to do with the variety of popcorn used, or if it's something added to the popcorn before storage.