Thank you for the step by step breakdown! I follow now.
Here, from the S16 manual. Are you're two S16's set as master and slave as they are required to be for stand alone?
The on stage S16 must be set to Standard Mode and the FOH S16 must be set to Master Mode.
5. Standalone Operation
The S16 does not necessarily need to be used in conjunction with the X32 console.
A pair of S16 units can be linked to send 16 channels to and from the stage,
providing a high-quality digital snake that can work with any analog mixer.
In this scenario, a master S16 will be placed at FOH near the main mixing console,
and the other on the stage (see ’S16 as standalone snake’ hookup diagram).
The†FOH unit must be set to SN MASTER mode so that it can control the preamps
of the unit on stage. All sends from FOH to the stage can be connected to
INTPUTS 1-8 on the ’master’ S16, which will appear at the on-stage unit’s XLR
OUTPUTS. Connect all the sound sources from the performers to INPUTS 1-16 of
the on-stage S16. Channels 1-8 will appear at the ’master’ S16’s XLR OUTPUTS and
channels 9-16 will appear at the ADAT OUTPUT. Connect the ADAT 9-16 OUTPUT to
an ADA8000 or similar preamp to provide analog XLR outputs. The outputs from
the ’master’ S16 and the ADA8000 can be connected to any sort of main console
for mixing, analog or digital.
For recording applications, a single S16 can also be used as a high-quality mic
preamp. Connect the sound sources to the INPUTS 1-16, and send those channels
via ADAT to an interface or ADAT card installed in your computer. For this scenario,
the S16 must be set to SPLITTER mode.