I will make the assumption you are behind a firewall at home.
Do NOT do this setup if you are not behind a firewall!
I will also assume your not using any type of windows based domain.
If that is the case this is simple to setup.
Create a new user on each local PC and call it what ever you like but in this example call the user "subsonic" Give it a decent password and make it a local admin just in case. It will probably work OK as a reg user but for this setup make it a admin. You can always reduce it back once you get it working.
Then on each PC create windows shares to each music library you want to have in your collection and allow this subsonic user FULL access to the share. For example: HerTunes, HisTunes
Now on the computers your running subsonic change the service to login as this subsonic user. The trick here is the service will use this ID to reach out on the network. Be sure to restart the service after making the change.
Now jump in subsonic and update the "Music Folders" location to point to these new shares. On your PC setup the link like so: \\hercomputer\HerTunes
Since you have files local you can retain the the local drive definitions but using the UNC name here you can scan and index those files on that remote share.
Force a index update and watch the log. You will see subsonic reach out and index those remote files.
I have a PC setup in my living room that uses this method to connect back to my main server PC that I stream to the Internet with. I currently index 186 gig this way and it works well.