It's been a looooong time since my MP-1 days; however, I always find 4-band stacks too limiting.
What I would prefer in most processors would be a 6-band stack, placed right after the preamp section:
a lo-lo, centered at around 70 Hz or so, partly for handling dives, partly for use with 7/8/9 stringers
a bass, with programmable center and gain
a mid, likewise with center and pain, but having a higher Q / narrower bandwidth when lifting it above, say, +6, to better accentuate those defining mids
ordinary high and presence
an additional 6-7 kHz filter, to be used for 'fizz-off' on distortions, and for lifting the upper harmonics for cleans
Now, this weren't what you [MJMP] asked about. So for the MP-1, as I remember it, the tonestack worked fairly well.
Keep the presence and high filter as-is, and just see if you can add my above mid- and bass ideas.
That is, those would be my ideas, of course. YMMV, as usual..
A note on the MP-2: While the extra 1/3rd octave EQ is nice, at times I really find it somewhat annoying fiddling around with all 13 EQ frequencies.
Well-laid-out voicings combined with afore mentioned 6-band stack ought to be enough.