Okay, so got fucking around with the JMP-1. I bumped up the value of R124, which is the cathode resistor for the second tube, first gain stage. I came upon a post from Trace from Voodoo Amps on a forum somewhere in the depths of the internet and he mentions that most of the clipping happens from diodes, which seems to be common knowledge from everything I've read. What I didn't know was that only 1 tube (2 gain stages per tube) is for the OD channels, and 1 tube is for the clean. I figured that's perfect, I like the cleans, just want more gain on the OD channels.
Swapped that resistor for one I ripped out of the MP-1, was originally a 2.2k, bumped it up to 7.4k, trying to up the resistance on the cathode, which makes it a cold clipping stage which is kind of the SLO signature thing that everyone copied.
Ended up a partial success, the OD2 channel is louder for one thing, has slightly more gain, and is WAY more dynamic in response to picking. OD1 didn't change at all, which leads me to believe that OD1 only uses the second gain stage of the tube to go into the tone controls.
I'd like to push it just a bit more, so want to put in a higher value resistor, maybe 10-15k, see what it does. I just used what I had on hand to see if it would make a difference. I like what I'm hearing though, so that's promising.