Digital studio · declared evidence
Which device leads—and where does its clock go?
Plan one leader, one follower and a real ADAT, S/PDIF or word-clock timing path, including a return path opposite to audio.
Your declared setup
Audio direction and clock direction can differ
Suppose B is an expander sending ADAT audio to interface A. With only B OUT → A IN, B can supply the embedded timing only if both devices support that leader/follower arrangement. Choosing A as clock leader requires a supported return timing path to B, such as A ADAT OUT → B ADAT IN or a documented A Word Clock OUT → B Word Clock IN route.
A dedicated BNC cable does not carry the eight missing audio channels. Conversely, an output-only audio connection cannot act as that device’s incoming timing reference. The planner shows required settings and missing routes, not a measurement of what the equipment is currently doing.
Exact-model clock constraints override the generic plan
Not every interface can slave from its optical input. Apogee’s Quartet documentation is an explicit example of a receiving interface that must remain clock leader. Check each device’s source choices and firmware before applying a proposed plan. For BNC, audio sample rate and transmitted word-clock frequency may differ under documented base-rate modes; distribution and termination are outside this two-device worksheet.
Sources: Focusrite clock sources, Apogee fixed-leader exception, RME word-clock rate modes. Asynchronous sample-rate conversion and multi-unit clock trees need a different model.