I worked with the characters to create some compelling back-stories that wove in the campaign traits and the reasons they were in Kenabres. On the morning before the ceremony started each one of them got a minor gift for Armasse from an NPC character in their personal story.
I ran with the text from the AP and also borrowed and edited in text from a few campaign journals that I've read (and thanks to any authors I plagiarised) but had a carefully structured pattern to how I revealed things.
1. I played a theme tune for the campaign (Main theme from Diablo III soundtrack) and read out an opening paragraph about the horrors of Sarkoris.
2. Then under some quieter atmospheric music I gave them all the backstories (around 1 page of A4) for them to read. That got them all thinking about their characters and past.
3. I read out a section about Armasse and what it means for the city of Kenabres.
4. The players turned over their sheet and read what they had done that morning, see section below. Then they had all made their way to the plaza and had climbed the steps of a statue for a better view of proceedings. That finally set the stage for the big reveal.
The Cleric of Iomadae who was a Mendevian wastrel until his sister was killed. He was at the Cathedral and being invested as an initiate, he also intervened in a dispute between some of the fanatical witch-hunting 'Burner's and other of the faithful. He was given a silver rosary of the Acts of Iomadae. Our Kyoninian Menhir Savant druid studying leylines and ancient Sarkorian traditions was in Truestone Park with Crocis who tends the garden. Crocis gave him a remnant of Sarkoris, a mammoth ivory tusk scroll tube engraved with symbols of the Green Faith.
The Pathfinder Society catfolk bard is part of a small team infiltrating noble society in the city and she got a sheaf of Angel Quill arrowheads from her superior. We have a Dwarven healing focused Witch who is in the city as part of the war effort supporting the Holy Legion of Torag, she got a home-brew pair of Minor Healer's Gloves (+2 competence bonus). Finally the Hellknight (Order of the Godclaw) completed some trials of combat and was accepted as an Armiger and given a steel and ebony inlaid breastplate by a commander of the order.
5. Then I hit them some more dramatic music and ran sound effects of an earthquake and an ear deafening ringing and read them the shocking piece about where they were in the vast caven.
6. The final piece was the slow piecing together of their memories of the events in the Plaza as written.
All my players sat there in shock and were immediately immersed into the seriousness of their situation.
As a DM setting the stage with some written text that gave the players the time to create their own mental pictures really helped build the sense of the opening section of the AP. The horrors of the Worldwound, the morning of Armasse, and then the shock of the attack of the Wardstone and the destruction of Kenabres really created an impact.
Here's a link to the script I used with the sample text for the cleric in the campaign. https://drive.google.com/file/d/0B9ZyjcaqPRoEVzRhZzVqS0pnRkE/edit?usp=shari ng
I also kept aftershocks and waves of demonic energy from the attack running for the next three hours and all of the vermin in the AP seemed to be infected with it. That's got the players really worried.
I hope some of this proves useful.