A quick, Low Spoiler guide to how to use the new room included in the DLC and get it working for you as fast as possible.
The Souls Room is unlocked by the bonus corpse after you progress through the Bishops quest to obtain River Sand. You must then repair the three broken machines in order, while also renovating a room for your new guest. It’s worth doing so as soon as possible, because you cannot really benefit from the room until all three are completed. Meanwhile there are two chest slots and a workbench that you also desperately need.
There is also room for single pallets, which are functionally useless in the room but do raise the max points. You can also safely ignore the soul containers because they cannot be upgraded to higher marks, so you may as well wait until you complete the spirit tech tree. These can be built at your leisure but are not needed for the room to work.
The questline is optional once the machines are built, and you can fully upgrade the Soul Healer with it’s extra sin slots as soon as you send through your first handful of souls through the process.
The Soul Extractor
Every corpse has a soul that starts at 100% and quickly fades until it cracks apart into a Sin Shard when the body is roughly at 70%~; at that point it must be extracted from the autopsy table like anything else. When you get a new customer, throw it into the extractor to get a Harmed Soul, then shelve your corpse in the morgue. This “Check In” Process will become an integral part of your nightly intake.
ALL corpses have souls, including the ones that you buried before unlocking the ability to perceive Souls and Sin Shards. So they are all sitting there with a Sin Shard in them, even if you stripped everything out.
The Soul Healer
This machine uses organs to clean souls of their sins in order to go to the land of the dead. The first jar uses Flesh, and eventually you’ll have to slot every kind of organ in. Until way later in the game, this machine is the only way you can find out what the point values of organs are. Also, once you set the machine up, it will just work until you add new organ slots that must be filled. You’ll get a Sin Shard for each sin you cleanse properly and a Healed Soul for every Harmed Soul you put in.
The best I have figured out is that you eventually need good, modified organs to have a great success rate and thus get the full 7 shards per corpse. With minimal tinkering, I have a 80% success rate and that’s more than enough shards to do voodoo. I noticed that later on in the story, the process needs modified organs for a better rate.
A new prayer exists in the tech tree that will yield more shards that you will need if you want to really take advantage of the process.
The Soul Portal
Healed Souls get sent to the afterlife and give you the soul points you need to fill out the new tech tree and use the new remote control mechanic. These soul points let you remotely set up tasks from the map AND you get the experience points for the work. Later on you can build the Soul Container Mark 3’s and store extra souls for a time in case you have too much soul power.
The better your Healing process, the more bang for your buck you get. I found that the points stack up fast and can be used just as quickly.
The Workshop Table
The reason why we want Soul Shards is because they are used for crafting basically everything progression related. Besides modified organs for optimizing corpses you can skip alchemy and make silver/gold fertilizer, and even produce a few new prayers!
A core part of your process is using a few corpses exclusively for spare parts so that you can upgrade them in the Souls Room. You can then remove low value parts and shove in better, upgraded parts in order to fine tune their skull values. Yo can also fine tune your zombies using this process to get very hard working undead.
In addition, once you get this process started you will unlock two wall mounted cremation ovens! So you can just rip apart corpses with glee then dump them into a proper oven without having to go outside.