Hi Casey

> That said, I got mine used with this mod already done, but I have no
> idea what it is for! Can anyone please have a look and get reply to
> this post

The picture doesn't say too much. It would be more helpful to open the
MonoPoly and take a shot from the inside to show where the cables go to.

There are a lot of possible moddings:

CV/Gate-out CV/Gate-In for the individual VCO-voices.

Separate triggers for the VCO / VCA Envelopes

The width of the connector also implies access to the keyboard matrix,
which would enable additional MIDI-In/MIDI-out interfaces.

...

Florian