It sounds like the parts of your system are running at the same nominal sample rate but are not actually synchronised. This will cause the occasional click you describe.
When you say you tried syncing the H8000 to the Kore interface, what did you actually do ?
You could try setting up the Kore as the sync master (ask them how to do this) and sync the H8000 to the spdif output you mention.
I'm not familiar with the Kore unit so can't advise you on it.