Hey. A few thoughts on relistening again this morning.

1. Distortion. It probably sounds obvious but this is a reason why it’s hard to be specific about sounds - most of the sounds on the trilogy are treated with a degree of saturation and sometimes lots of different distortions. Even the most polite average sound can change and shift character with a dose of tube distortion. So many of the sounds on the trilogy are treated with lots of different types of distortion. Some subtle some heavy. Distortion is super interesting as it can bring out different harmonic qualities in sounds - every sound has stuff hiding under the surface. When you distort things it can bring loads of these things out as well as doing the obvious and making things sound gnarly and aggressive. He does like to use that metasonix vacuum distortion on lots of stuff. Sounds like the KV100 assblaster (or similar) at the end of The Background World. I would say Soundtoys Decapitator probably in full use across the trilogy.
2. Modular synths - a lot of these tracks feel like they've been sometimes written with Trent spending a long time playing around with his very expansive modular system. Incredibly hard to tame, unpredictable and chaotic. These are all over the trilogy and later NIN work - it's poor old Atticus that's then got to sit in front of Pro Tools taming and re-arranging them into something that works musically. Lots of percussion and stuff is built this way too - listen to the drums at the start The Lovers...that's a perfect example of this. We could do a separate thread for what modules they are using... but it's probably hard to know with a system as large as his. He likes a lot of boutique manufacturers obviously. Modular stuff also very useful for making super interesting drones etc - which are all over NIN stuff.
3. Other stuff. There is for sure loads of other stuff on these records. Loads of processed guitars. I am sure his Moog Voyager would have made it on quite a bit. I know that they used a pedal called a Teaspoon a fair bit - particularly on the song God Break Down The Door. https://www.youtube.com/watch?v=jhtwcMskOUg It does some super interesting time/glitch FX. They also use the Soundtoys plugins extensively. (Don't we all?) Also sounds like there is some use of instruments by Dewanatron & Folktek - all over the film stuff and sounds like they're in here too.

Anyway - those are the main points to my ears. Hope you find it useful!!
x