I stumbled on this while looking for flipflop octave divider circuits. I figured the 4013 dual flipflop would be fairly simple to use to get a sub-octave square-wave for when we want to fatten our oscillators and might make a good easy brAEdboard project for newcomers to DIY.
More generally, a guitar signal needs a little boosting to feed into the Master module's input. Any guitar pedal that ups the signal a bit would do (EG, fuzz etc.).
Using a guitar pedal as a module would need two converters: one to drop the AE 5v~ signal down to about 25mV~ for the guitar pedal, then another to take the output of the pedal and boost it back up to 5v~ to continue through the other AE modules.