so on my cheat sheet, i cropped off the connection details for the cm108 fob.
on the round mic jack, pin 3 is your PTT connection
pin 5 is ground
rx and tx audio as marked on the mic jack
no problem wiring these to a trrs plug for the digirig audio side.
(obviously selecting comport ptt ‘rts’ instead of any cat control ptt command)
stay away from pin 6 !
it is +v and you don’t want to touch that to any ground
good luck
kb0wlf
73