This page is a summary of how to connect two audio interfaces via ADAT.
The original forum discussion that inspired this article is:
https://forum.audiob.us/discussion/43224/audiofuse-alternatives
Another related Wiki post that relates to this is:
https://wiki.audiob.us/doku.php?id=digitally_routing_audio_between_ios_devices
The main points to a successful connection are these:
The process for setting up the ADAT channels on the audio interfaces will depend on the device manufacturer, but will more than likely be via control software installed on a computer. For example the settings for the Arturia AudioFuse are changed through the Arturia Control Centre software installed on the computer and Focusrite have their own control software that is also installed on a computer. It's worthwhile verifying that the clock source is set up correctly on the computer while the interface is connected there. This is achieved on a Mac through using the Audio/MIDI app found in the utilities folder to select the audio interface you want to check. the clock source will be visible here.