It appears that the character voice clips are in NLXWB files. The NLXWB files for the music and whatnot are apparently unencrypted, but the ones containing voice clips
are encrypted, unfortunately. It doesn't seem anyone's made a tool to extract from these archives, nor do any pre-existing tools that I can find support NLXWB files of any kind (the unencrypted ones have only been extracted through hex editing).
Would it be possible to create a script of some kind to extract the files inside?
To anyone who may be interested in trying to make something to extract these, I have included the files for Luigi: an NLXWB file and a RESBUN file, as well as a BUN file that other forum posts have led me to believe may be useful.
CHAR_LUIGI_Sfx.zip