I don't think I get what you mean by "manual script calls" - do you mean trying to access the functions directly through the "Script" command in RPG Maker? - I think what you're actually asking for is the ability to use a variable (or some sort of evaluable JavaScript) in the plugin command to refer to an event, instead of hardcoding it. This is a feature I could consider adding if so.

I did not design the plugin around calling the AudioManager.playFocusedSE function directly from outside the plugin, but if you really insist it could be done without any updates. 

Option 1: In MV format the "args" as a string exactly like how you would call the script in the first place. (This would be simpler in MZ, where the args are passed as an object, rather than a string.) 

Option 2: Don't include any sort of location/event data in the args whatsoever and pass the location of the event you're trying to use as a source to xCoord and yCoord. The other args would still need to be set up correctly.

Option 3: If you have the event object in your code as, let's say "loudEvent", then call "loudEvent.playFocusedSE('the parameters you would give to the plugin command')", which is what is used for custom move routes; this would need to be a formatted string even in MZ.