I saw the following on Arron Nelson "Simple Mods" page seen here
http://www.diystompboxes.com/wiki/index.php?title=Simplemods#Simple.2C_Easy_Mods.2FTips_.26_Techniques (http://www.diystompboxes.com/wiki/index.php?title=Simplemods#Simple.2C_Easy_Mods.2FTips_.26_Techniques)
It Says Simply add back to back (anti-parallel) diodes from signal to ground after the output cap to turn a booster circuit into a distortion circuit. you can put the diodes anywhere on the output as long as there's a blocking capacitor before the diodes. You can put 2 diodes or 4 for more output. You can also use germanium diodes or silicon diodes.
Can I just put two sockets directly on each of the output jack lugs and try different diodes in opposite directions? perhaps make these switchable? ( not sure how to wire that though :-\
when one half of signal say + portion of wave reaches the diode threshold, signal above that voltage is shunted to ground...event...harmonic. every wave cycle now has these 'event' [switching on near the top, switching off near the top as the wave begins it's descent to...
Same thing except on the negative wave portion if there's an = threshold value and the signal is perfectly symmetrical.
Fun to play with, Ge's have the low threshold [you'll probably meet that voltage easily, and hear the difference in M-booster].
I'd guess because that Mosfet boost swings clean and big, you might want something toward the high threshold, mild clipping, perhaps the suggested HF taming across diodes, or other.