Here’s a scratchpad on how Jacktrip Hub Mode does audio routing as of early September 2020.
Starting the server in Hub Mode (capital-S instead of lower-case S) with the “-p” option offers four ways to configure the server. Here’s an example launch string that would fire up a server in Mode 2:
jacktrip -S -p2
Mode – 0 (the default – my machine hears everybody and everybody hears the mix that I send them)