its easier than that. Moon reader can directly connect to calibre OPDS server. its almost as as good as going via the app.
there are threads somewhere ( in CC subforum) with how to do it - I used them myself. you basically have to add OPDS to the end of a URL and point moon at it
the SD card think should also work, but not a virtual drive e.g. I put pcloud onto my tablet and copied my library to pcloud but CC can't find that.
instead, i used a library copy in dropbox and the app called calibrebox from play store, for when my library pc is off ( because cc cannot authenticate with dropbox on a new tablet)
if you are stuck I will look up what OPDS settings I have in moon
edit - here from the other thread, I have a bad case of dyslexia when it comes to that server
Please note it's OPDS, not ODPS. That might help with searches.
It's built-in to the Calibre content server. Address to the feed would just have opds at the end:
http://<ip_address>:8080/opds
On Moon+, you go to Net Library >> tap on the 3 dots on upper right corner >> Add new catalog >> Calibre IP