Since 2018-11 we use an Arduino MKR Zero with an Ethernet Shield to control the mux.
This board has the pinout for the MKR Zero, and prvovides 10-pin IDC headers for two ribbon-cables to the Mux-boards as well as two front-panel status LEDs and two Buttons.
J4 and J5 provide the 14+14 pin connector for the MKR Zero
MUX1 and MUX2 are 10-pin IDC headers for ribbon-cables to the MUX-boards
PDF of the Schematic, PCB, and Gerber production files can be downloaded below: