Until DA4 comes out I'm just going to continue to headcanon The Box of Screaming in DA2 as the place where the Evanuris were actually locked away lol.
A lot of people never got this codex! :O Here you go!
I received the box from a man I met in the Silent Plains. He spoke little and would not reveal his name. For reasons I shall not detail here, I had been kidnapped and left for dead in that gray, wind-blasted wasteland.
After days of walking, I was parched and close to death. I was about to dash my head on a rock to speed my passing when the man arrived. He possessed a waterskin containing ample water for a person traveling from our location to the to the Imperial Highway. From there, he said, I could find my way to Solas or Perivantium. He offered to give me the waterskin if I agreed to take three things from him: a glowing crystalline shard, a bronze sphere, and an iron-bound box with no hinges.
I asked the man if he wished to have these items delivered. He said that he merely wanted me to have them. It was an odd request, but I was too weak and too desperate to think much of it. And so I agreed. The man put the items into a leather sack, which he handed to me along with the water.
"What about you?" I asked. He said nothing, only pointed in the direction from which I had come. "There is nothing that way," I said. He merely smiled at me.
I found the Imperial Highway about a day later, and a caravan driver agreed to take me to Perivantium in exchange for the large glowing shard. In Perivantium, I bartered the bronze sphere for new clothes and room at the inn. That night I examined the iron-bound box and found no way to open it. I held it to my ear, and thought I heard slow, measured breathing coming from within. My mind was afire with curiosity, and I obtained from the innkeeper a large hammer, thinking to smash the thing open. The moment the hammer touched the box, it shrieked—the shrill sound pierced the depths of my soul.
I gave the box to the innkeeper in the morning and felt better for having rid myself of it.
—A page ripped from a mysterious journal, on display in the Black Emporium