Gustard C16 clock

Stupid question of the day... 

I have a Gustard R26 dac and a Gustard U18 ddc.  I've read comments from users that say that adding a C16 clock adds a bit of improvement. 

For the life of me, I can't figure out how a C16 connects to the U18.  I know there is a cable with bnc connectors.  But, I only see outputs on the C16. Six of them. Some direct and some isolated.

Is the single cable bi-directional? I'm used to sound going in on one cable and out another. 

Anyone using a similar setup that has insights on what I might expect for improvement (if any)?