Hello and welcome!

> I am very much intent on getting a combination of the units above for
> processing duties, my question is there any overlap between the four
> selected

Let me describe it soundwise:

The A116 can sound similar to a simple fuzz box, but has many setting,
which can make the sound "thin". I like it for non-synth signals and for
classic TB303-Filter-through-distortion-box sounds.

The A136 can create sounds which remind to hardsync, but also normal
"fuzz box" sounds. So there is an overlap with the A-116.

The A137 is basically four stages of A136 in series, with less
parameters per stage, but the count of stages adds parameters. It
doesn't really do the fuzz box sounds, but it does all the hardsync-like
waveshaping sounds in "cubing".


The A-137-2 makes a supersaw from a normal saw. It has nothing to do
with the other three modules.


The A116, A136, and A137 require that you thinking goes away from
subtractive synthesis. Those modules add(!) something to the sound,
while usual filters subtract(!) somthing from the sound. To get the
interesting results, you have to feed smooth and "dark" sounds into
those modules.
Of course you can use those modules for alread bright signals, but then
they do not add a dramatic change to the signal. Example: sending a
rectangle wave into one of those modules is quite senseless, as a the
distortion of any waveform will result finally in a rectangle.

To be honest: 80% of the sounds from a A116 or A136 can be achieved with
a simple guitar stomp box. In the opposite the A137 (used in the right
way) can create very unique sounds. I recommend the A137.

Florian