Chuck Schuldiner

In this source it says he did in fact use a DS-1 and also the quote below confirms chuck used a boss

On the first 2 Death albums I was using a distortion pedal from Boss, but now, using a Valvestate, I don't need it anymore. You can plug in your guitar directly in the Valvestate and still have a great sound. When we're in the studio it takes no more than about 20 minutes to get a good guitar sound. - Chuck Schuldiner

The Empty Words Project is founded by Chuck's family. Here they republish an interview with Pit Magazine, originally published in June/1999, Chuck Said: "My amp is a Marshall Valvestate head and cabinet, that's about it. I don't use effects except for a little chorus on my leads, I really like a basic setup." This article from Guitar Geek confirms this as an 8100 specifically.

This rig diagram shows that Chuck used 10-46 GHS Boomers.

This rig diagram, on Guitar Geek, shows that Chuck uses DiMarzio X2N bridge pickups on his B.C. Rich Stealth guitars.

During the "Human Tour of the World" in the early 90s, Chuck was miking up a Gallien-Krueger model GK-250 with hollow stacks for appearances. Aditional info: https://en.wikipedia.org/wiki/Chuck_Schuldiner

The guitar he used for the majority of his career [...] was a B.C. Rich Stealth. Also The Empty Words Project republished an interview with Pit Magazine, originally published in June/1999, Chuck Said: "Well, I really have a simple set up. I've been playing the B.C.Rich Stealth for years now. I have three of them, one is a custom black one that is my main stage guitar, one is an emerald green that is really beautiful, and an old one that I recently stripped down. They all have a fixed bridge"

This rig diagram, from Guitar Geek, shows that Chuck used Dunlop Tortex Standard 0.88 mm picks.

In this image, Chuck is playing a green mockingbird

You can see the amp at 0:12

Chuck can be seen here posing with a B.C. Rich Ignitor.

According to this rig diagram, Chuck used a Marshall Valvestate 4x12 cabinet.

In this user-uploaded photo, Chuck Schuldiner is seen with a Rickenbacker 4001 Mapleglo bass.

At 00:54 into the video we can clearly see Chuck using a JCM 800 stack.

Chuck sitting in front of his Valvestate Cabs

In the YouTube video titled "Death - Iguanas, Tijuana, Mexico: Spiritual Healing Tour (October 6, 1990)," Chuck Schuldiner is seen using a Marshall JCM 800 2210 guitar amplifier head. The amp is clearly visible to his right, especially at the 1:00 mark.

Chuck Schuldiner is confirmed to have used the Boss SD-1 Super OverDrive, as evidenced by a Death fan and collector, Alex Wad, who possesses a unit previously owned by Schuldiner.

Chuck Schuldiner is seen playing an Axtra Prophecy guitar, custom-made for him, equipped with EMGs instead of his usual DiMarzio X2N pickup, as evidenced by the image provided. 

In the 1990s, Chuck Schuldiner used a DiMarzio ClipLock Strap on one of his guitars, as documented in the YouTube video "History of Chuck Schuldiner’s Guitars" by fr0gst0mp.

Chuck Schuldiner used the Ibanez RS440 Roadstar II Deluxe guitar during his brief tenure with the Canadian band SLAUGHTER. This is evidenced by a photograph showing a guitar identical to the one Schuldiner is known to have played at that time.