Ok so what I think you're trying to do is add speech samples to supplement the text.
(I'm using example paths and so on, but just substitute for your data structure).
On start of period "blah1"
Xaudio2 autoplay file "Audio\Speech\NPC\bob_blah1.wav"
Play the sound file.
Set Variable_Holder_SpriteObject.value('Last_Speech") to xaudio.lastplayed
This saves the number of the last channel in a variable holder object, substitute with a global if that's your preference. This is so that you can stop the specific sound playing if the player skips this line of dialogue.
Dialog_text write "What began as a conflict over the transfer of consciousness from mind to machine would escalate into a war that would span over 4,000 years, and destroy thousands of worlds"
Type the actual dialogue into the text box. Adjust speed to match your sound file.
On end of period "blah 1"
Xaudio stop channel Variable_Holder_SpriteObject.value('Last_Speech')
On start of period "blah2"
rinse, lather, repeat.