Hello -
I have been successful connecting my iPad to the YACReader Library running on my Mac (on my local network), but I would like to access my comics externally. I have an external URL that connects to my local NAS (where the comic files are actually stored), but I am unable to determine if this is supported. Is it? What protocols (if any) are supported, and how/where would the connection be populated in YACReader on my iPad?

You can install yacreaderlibraryserver in your NAS and then access to it using your public IP + a forwarded port

Check the linux seciont in this forum, there are some tutorials about how to it.

Or you can let your mac on and connect to that machine using the same method, public IP + a port configured in your router that points to that mac.