Ah yes, the Marshall JMP-1 preamp. I had bought one in the 90's when they first came out. First I paired it with a MosValve power amp which I hated. After that I tried it with a Marshall 9200 with 5881's, all through a straight Marshall 4x12 with, I think, 75W Celestions. With the 9200 it sounded great, but the rig was ridiculously overpowered for my needs. Back then I didn't know the millions of things about guitar amps I'd eventually learn on usenet forums.
I liked driven sounds on the JMP-1 but the clean was just fine for my taste. Eventually sold the whole Marshall rig and replaced it with a Matchless DC-30 which I have to this day.
I did buy a Fractal FM3 which has JMP-1 models onboard. It was fun to revisit those tones and I was able to recreate tones I recorded back in the day, but I think I can dial it in a bit better now that I'm more experienced.