Hello Andy Sorry form my bad English, i’m from Holland.
I don’t understand your setup.
But it depens on witch AES50 port you use on your mixer, have you put your S16 in port A or B.
Then go to routing menu tab Card out and select the local inputs 1-16 and AES50 A1-8 or B1-8 for channel 17-24 and A9-16 or B9-16 for channel 25-32
also set usb card on 32 / 32 in menu > setup > tab card foor play back