Is there a way to include speech within the "Display" command
Example:
Display ("&1 Cheese ruins lives.");
And if so, what would the sound's filename be?
Yes, look for game.narrator_speech global variable in the manual.
game.narrator_speech
Which character ID to use for voice speech within Display() command. Default initial player character. You can also use -1 which uses 'NARR' prefix - special narrator character.
Example:
game.narrator_speech = -1; // using NARR character
So Display ("&2 Hello!"); shows a message "Hello!" and plays NARR2.WAV file.
~Cheers