Here is how I have everything set up:

XScene is a two actor conversation in an interior cell and part of a quest. The scene contains only back and forth dialogue between the actors and has no actions/movement set up for either actor (besides the speaking parts).
-both actors have been assigned quest aliases
-scene is set to run on stage 25 of the quest
>stage 25's fragment is:

XScene.Start()
SetObjectiveDisplayed(25)

-there is a triggerbox near the location of the scene that has two conditions: 1)the player to walk into the triggerbox, 2)the quest to be on stage 20. When these conditions are fulfilled the trigger script sets the quest stage to 25

Now my assumption was that once the triggerbox goes off, the scene would play. The trigger seems to be working fine because my stage does advance to 25 and objective(25) is shown on my screen. The two actors, however simply stand there and say the standard npc idle speech for their voice types. The actors also seem to be working fine because I can engage them in combat and they act normally.

I tried to test to see if perhaps the scene was running but the dialogue was not displaying. I did this by adding an NPC cast spell action (summoning atronach) to one of the scene phases, but still nothing happens. What am I missing/doing wrong?

Did you record audio for the scene? Without audio for the involved lines scenes dont work at all.