Was watching this video on Alice in Chains Man in the Box recording with the original producer/engineer and he said they used three things to get the distinct guitar tone: Randal 2x12 combo amp for mid, Marshall (possible plexi, couldn't remember exactly) for low end, and a rockman for the high end. Thought that was interesting.
At about 9 min in he talks about guitar eq frequencies and at about 10 min he talks about the Rockman. Just says "one of those Rockman boxes", so X100, Compressor, DG, who knows.