I have the same setup - you can do as Trevoire told you... OR, if you prefer your Saffire to be the master clock generator (somehow I trust Saffire more Than Behringer), do the following (and you'll need TWO optical cables):
- On Behringer set the Sync to Slave and ADAT In
- One cable goes from Saffire's ADAT Out to Behringer ADAT In (this cable will carry the clock sync signal)
- And the other cable goes from Behringer's ADAT Out to Saffire's ADAT In (this one carries the actual ADAT channels)
- In Mix Control set the Sync Source to Internal
That's it!
Good luck