just to make sure you understand a couple of things
You can play anything on a client. To use the client as the controller you have to load the library from the main PC (the PC running media server). You should see the library under the tree in Playing from. The music doesn't have to be playing at all on the "main" PC.
You can also control playback from the server PC from the client (no playback on the client) OR you can as you have seen control and play the same or different music at the same time. You only need to link zones when you want the same music playing (you probably have to adjust for it to be more or less in sync, but one step at a time
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Why don't you check in Options=>Network=>Client Options (on the client normally the the use DLNA to share is not checked btw; uncheck it at least at first) and make sure that show playback zones is checked. By Default the remote zones will show "THERE:" before the zone name. The default zone I believe is Player, so you might see "Player" and "There: Player". You might also want to rename the server library from the client (only on the client!) and call it something like Downstairs or HTPC to make it more understandable as each installation of JRiver will have a Main library which is really the default "local" library.
Then from the client right click and link the zone. You can see what is playing or is queued to play in each zone by clicking form the tree on the left under playing now the "Overview" button. If you see the zone or zones created on the client AND on the server you are good to go normally. There are some tricks in sending tracks from one zone to another - experiment with right click on selected songs Send To and you'll see
If you load the server library it will be remembered when you reboot JRIver on the client. This can be done either from the tree or from File =>Library. This wil also permit you to tag your files and do most operations (not all) from the client.
No real guide, I can post a link but if you have music playing and can the music server setup is ok probably for now.