Originally Posted by itimpi
In calibre2opds it will only support the main Series field so your approach is probably the best way.
What you might want is to set up a custom column in Calibre of a "series" type. You can then use that to record the sub-series details.
Tried these but then lose ability in C2O to list other books in series on web page :-(
Each book then shows as separate series as series names all different :-(