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.
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