Syncing DIF-AT box to sound card via ADAT

[tomatoKetchup]

Hello,

Just bought a DIF-AT box to interface between my XV-5080 and my sound card (an RME Raydat) via ADAT. I'm trying to figure out if ADAT synchronisation of the DIF-AT to my RME can be achieved via the optical IN cable (like most ADC would allow) or do I absolutely need to use the SYNC (D-sub 9 pins) connector?

Thanks for helping!

EDIT: alternatively, could I achieve syncing between the XV-5080, DIF-AT and the RME card by sending a word clock from the RME to the XV-5080 via BNC cable?