Hi Tolriq,
I’m a step further with my one DB setup instead of 4 
I’ve got my kodi-headless up and running (mysql) and my media is added with sources.
If I now add the headless server as a host within Yatse, all is fine. The only reason I’m adding the headless instance to Yatse is to base all other hosts on this one within setting (use central server - mysql).
If I now add one of the clients to Yatse and set it to be based on the headless-host within Yatse’s settings, it syncs, but:
If I chose a source within music artists, the artists get filtered and only the source’s artists are displayed but have no albums!? It’s always “no media” or “syncing, pls wait”. If I choose no source (choose remove) and search for the same artist, all albums are displayed fine.
This even works within the headless host, but not for the clients?!
And a short question for my understanding:
I thought that if I choose one host to be the central host and add another host based on this (already synced) host, the syncing will be done against the central host, not the client?!