The set of acquisition relations needs to be expanded to support the pertinent audiobook types to be sure that they actually "appear" in the Catalog. They would otherwise be considered "unsupported" and be invisible, like PDF's.

Type signature on current method:

+ (NSSet<NYPLBookAcquisitionPath *> *_Nonnull)
supportedAcquisitionPathsForAllowedTypes:(NSSet<NSString *> *_Nonnull)types
allowedRelations:(NYPLOPDSAcquisitionRelationSet)relations
acquisitions:(NSArray<NYPLOPDSAcquisition *> *_Nonnull)acquisitions;