Been messing around with this, and discovered to record from the S16 you need to set the card output to S16,1-8, and 9-16 (for recording the 1-16 channels.
Recording the USB was a little tricky.
I had to move the USB L and R from where they were to where AUX 1 and 2 were, and select source there as USB L and R.
Then I need to make sure the faders were up, otherwise recording didn’t happen.
Hope this helps anyone doing this sort of thing.