One issue which I'm curious to see if you can address - the Special Edition alters a few lines of dialogue; the "Nice <object name>" lines are replaced by various takes of Guybrush saying "Nice!", and the lines for when Guybrush inhales helium from the balloons have been altered (presumably for copyright reasons).
Obviously if you're using the Special Edition audio, the text will have to be made to match the audio unless you want unvoiced lines (unless, in the case of the helium balloon lines, the originals are there too - both exist with filenames listed in the speech document that lists which line is allocated to which filename, though as far as I could see the actual files for the unaltered versions of these lines didn't actually get compiled into the game).
My question is - is it possible to introduce a check to see which mode the game is in (i.e. Speech Only / Speech and Subtitles / Subtitles Only) within the SCUMM script, to tell the game to do one thing in one mode or another if in a different mode? If so, would you be able to implement checks for these instances of changed dialogue, so that if you're playing in Speech and Subtitles mode the subtitles would match the SE audio, but if you were in Subtitles Only mode you'd get the original dialogue? = ) Could be good for completists if doable. Personally, I'd be happy just to have the SE dialogue, but I know some people would prefer the original to be in there somewhere, even if only accessible with voices turned off.