IIRC Alex Skolnik used an MP-1 in front of a 50W Marshall JCM900 for Souls, The Ritual and Handful of Rain....
Some Quotes:
How did you get your tone on the Testament album Souls of Black?
For some reason, more people ask about this sound than any other. It was my usual rig at that time which consisted of an ADA MP1 Preamp and Marshall JCM 900. I think any Marshall head will do, the only thing is it has to be set clean, as all your overdrive comes from the MP1. Usually preamps are put through power-amps, not Marshall heads, so doing it this way creates a lot of overdrive and it's a very noisy rig. But the sound was worth it. You shouldn't have too much overdrive on the MP1 either; a little bit goes a long way. Also, a pretty even balance between bass, mid and treble, not too much presence.
From "Guitar fro the Practicing Musician 12/94" (Savage Handful Of Rain era):
"Rhythm parts were played by both Jon and Alex using Criss Oliva's old Charvel Jackson guitar, dubbed "the Gargoyle." According to Alex, this guitar has the distinct sound of Savatage. "We had six rhythm tracks for each song, all with different guitars. Usually we ended up going for a track of the Gargoyle and a track of my Ibanez in the background," he recounts. "The Gargoyle sounded best each time for the rhythm tone, but the lead sound was my guitar and tone. A lot of rhythms were going straight through an amp Jon gave me, one of the best sounding Marshalls I've ever heard. When I ran my gear through it, we got a wide variety of tone. Depending on the dynamics, it reminded me of quiet Beck or when cranked up, like early Van Halen, which is my favorite tone in the world. This 50-watt JCM 900 from Thoroughbred Music was a dream amp. When Jon gave it to me I was speechless. I don't know if I want to take it out on the road because it sounds so good. It might just be a studio head."
"The result is that this record has some of the best tone I've ever gotten," Alex claims. "We ran it through the ADA MP-1 preamp, which I've used for years. Running through the ADA added a richer sustain sound, which is better for solos. In fact all I brought for this trip was a guitar and preamp -- there was my sound. I like a little dirt. I mean, I love Allan Holdsworth's playing -- he is a revolutionary player -- but he is so clean it's almost non-human. I apprecaite what Steve Vai does as well, but it's perfect. That's cool, but somehow Eddie Van Halen -- especially the early stuff -- there's this touch of dirt. There's a touch of slop that makes it more human. It sounds like it's on the edge. I like that."