Nevermind.
I was able to work it all out today. It’s not true that you lose 2 channels for L/R SPDIF. I have all 32 I/Os with my two 8 channel interfaces and Cubase recognizes all of them. One master and the other slave. Only the master is connected via Firewire. The slave is clocked via ADAT.
Check out this post. It was helpful for me.