I'm happy to say that after much debating I have finally settled on the first round of voice actors for the game. All of these voice actors are from the Voice Acting Alliance website, here's the list:
Male:
Isaac - Bothan Spy
Satan - Bothan Spy
Unnamed Man - DukeLovesYou
Jim the Skeleton Head - DukeLovesYou
Man in a Cage - DukeLovesYou
Priest - Steve Vito
Whispers of Depression - Greig Taylor
Whispers of Apathy - Greig Taylor
Whispers of Rage - Billy Ambrose
Female:
Temptation - Cayla Martin
Woman in the Mirror - Cayla Martin
Young Girl - Cayla Martin
Whispers of Depression - Cassandra Wladyslava
Whispers of Rage - Cassandra Wladyslava
Some excellent work here, here's a link to a quick preview of Brendan's rendition of the "Unnamed Man":
Things are moving along nicely, thanks all!