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.
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
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
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
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
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.