Working on a study for an alternative board, using  a slightly larger PCB with a 1x2 pin headers at the  middle of each edge of the board matching with the holes for the modulator shield.

The output connector should be changed to a PJ307 with a lower profile to compensate the extra height of the headers (compared to the previous version of the board)

Board Layout.  It was necessary to move some components and it looks like the lower right corner may need some relief to not interfere withe the power input jack.

PJ307

Pin Header 1x2