Has the CLI server changed from what it was years ago?
Back then, you had to start multiple servers.
Each ONE had a UNIQUE port and Library call out on the command line

(RTFM'd

) If you do not specify any paths, all the libraries that the main calibre program knows about will be used.
Of coarse, this might be a bit hard to setup on a headless system.
You need to do the equivelant of a Switch/Create: Use Existing to get the value into the configuration