General Walkthrough and Tips
When you first enter Cacophony, you will head up and be greeted by a Horde there. He will tell you Nerat is expecting you. Head right and open the Subterfuge (45) chest to reveal an Exquisite Blood-Soaked Mantle. Speak with Lyric and purchase the Sigil of Emotions. Then head up and left, looting the barrel and opening the Subterfuge (40) chest that contains healing potions.
Speak with Splinter to acquire the quest Opportune Offensive. Then speak with Wrathrot and Dirge and resolve their dispute. You can gain favor or wrath with the Scarlet Chorus and Tunon, so choose wisely. Be sure to inquire about the Sage to obtain the Sigil of Influential Domian.
Next head right and speak to Requiem, Gnashing Nils, Chaos and Calamity Gin and make a ruling about their dispute. Again you can gain favor or wrath depending on what you choose. Splitting the loot or giving Gnashing Nils half are both favorable options while the rest will gain you wrath or nothing.
Keep going right, up the ramp, and speak with Dalliance and Sickle Notch. If you decide to give them to the Scarlet Chorus you will gain Favor with them, but lose Loyalty and gain Fear with Eb. If you decide to put them in the pit you will gain 1000 rings, but again will lose Loyalty and gain Fear with Eb. If you execute them you will gain Wrath with the Scarlet Chorus.
Next head up and speak with The Voices of Nerat. You can gain or lose a bit of favor here and lose loyalty with Eb if you are not careful. Both your quests will now add addendums and you will need to speak with Seven Toes. Depending on what you decide to do first you will get the quest The Symphony of the Forge and be headed off to Lethian's Crossing, or you'll get the quest A Broken Chord and be off to Trapper's Junction.
Lastly, before you head out, speak to Chrysantha in the cage to the left of Narat. You will have to decide her fate and can gain favor and wrath with the Disfavored or Scarlet Chorus.
If you sided with Disfavored, you will need to assult Cacophony in ACT III. After you defeat the Scarlet Chorus soldiers, you will need to fight Voices of Nerat himself. During the battle, Voices of Nerat will switch its personality constantly, and each personality has different abilities. It will also summon his pawns, you need to clear them as fast as possible.
Once you defeated the Voices of Nerat, dont forget to loot the body.