Good news, everyone, good news! I also had this problem where NRPN things jump from 0 to 127 with nothing in between. Using Midi-Ox, you'll see that the Frequency Knob for LFO 1 reads like this:
B7 63 00
B7 62 25
B7 06 00
B7 26 00 <- that last byte will change as you twist the rotary from 00 to 7F (0-127)
So if you map the LFO 1 NRPN value (which is 37 in the manual ((25 in hex)) )
to your Akai or Novation controller and also monitor that output, you'll likely get this:
B7 63 25
B7 62 00
B7 06 00
B7 26 00
the difference being the '25' is in the first line instead of the second. I think this is why the Mopho freaks out. Oh, this is strictly my findings for the Mopho Keyboard. Not sure how different it is from the Desktop or the Tetra.
Okay, now for the good news. If you take the code and write it into the Roland A-Pro Editor like this:
B7 63 00 B7 62 25 B7 06 00 B7 26 DT
as a FREE MESSAGE
and make the Min Value 0 and the Max 127, whatever slider or knob you've assigned this free message to will now control the Mopho's LFO1 smoothly. Unfortunately I do not see a way to get beyond the max value of 127 and I don't know how negative values work in the Roland Editor... and you'll need to pick up a Roland A-300 or A-500 Pro Midi Controller to make this work. I tried NPRN with the Faderfox EC4 and the Midi Solutions Event Processor Plus but still got that 0-jump-to-127 error.
Assuming the Desktop module operates the same as the Keyboard version, the Roland A-Pro series appears to be the best choice if you want to control the Mopho strictly without Local control.
P.S. I was working on Midi Channel 8, so that's why it reads B7 instead of B0