Thank you CK,I texted Kahw just now.
His reply :
Cybershaft Opt21 > C1.1
SYNCHRO high Z
C1.1 > D1.5
SYNCHRO High Z
C1.1 is still the master for D1.5
Cybershaft is the master for C1.1
C1.1 + Opt21 serves as a master for D1.5
Both SYNCHRO 75 Ohm or High Z were using external clock as well.
HighZ Should be the suggested setting from CH.
When connecting with CH T1, the setting based on the manual is SYN 75 Ohm. It's good to know HighZ would sound great as well, and I will certainly experiment with both settings.