[Top Jimmy]

As you've discovered, you have a clock problem. The issue with the D8 is that it only has a word clock input and no output. So you have no way of syncing the two D8s with each other before going to the ADAT XTs. The master ADAT will clock to the ADAT input, the slave ADAT will clock to the master and the second D8 clock will be floating causing ticks and pops.

You can either find something to clock both D8s to or trade them in for the Digimax FS. The FS has word ins and outs so the second FS can slave to the first.