I'm just trying to figure out the best place/method of enabling automatic preloading for jplayer videos.

Function described here: http://www.jplayer.org/latest/developer-guide/#jPlayer-option-preload

With the various plugin/function/extension files (not to mention the ZP control panel itself) it gets a bit confusing as to where this and other jplayer options should be set.

Appreciate any help here...

You simply set options on Options > plugin > <your plugin>. Given the plugin provides options naturally. If it does you see on the list and also by an icon on the plugins tabs.

Maybe you can explain what is confusing by that?

However jPlayer has no option for preload right now so it uses the default "metadata". It is actually best practice IMHO not to preload unless the video is started since that could slow down if you have more than one video per page. Especially for slower connections or traffic limited ones.

If you like to have that option please open a ticket on Github.