Michael, we currently have a Mac Pro (Late 2013) running Reaper alongside an Apollo X8P interface. According to the manual, the Apollo x8p’s internal clock can be synchronized (slaved) to an external master word clock. This synchronization process involves configuring the Apollo x8p’s clock source to Word Clock within the Console application, connecting the external word clock’s BNC connector to the Apollo x8p’s word clock input, and ensuring the external device transmits word clock. Additionally, if the Apollo x8p is the last device in the clock chain, the Termination switch (#30) should be engaged.
Considering our setup, and applying your suggestion, I believe that by incorporating a DeckLink card into the other Mac Pro (Rack 2019) running DaVinci Resolve, we can designate it as the master word clock and synchronize both systems as we need.
Regards
Fernando