I think Calibre did it right with 1 file per format.
A Calibre Record is A BOOK, the same BOOK, regardless of file format.
If you have different EDITIONS or Languages, then they are DIFFERENT BOOKS and they need their own RECORD (

However the SERIES would have the SAME value, thus establishing a relationship to other editions)
2 Audio Books, assumes they were by different 'talent'. The metadata should match the content. (I guess you could make a case for a really reduced

bit rate version of the same performance)