Hi,
Unfortunately, there's no easy way to search through multiValueDictionary attributes but I would advice you to do so:
When passing KeyValueAttribute array, you can use any SQL statement as "value". In your case, only one KeyValueAttribute is needed:
new KeyValueAttribute(metaFieldName, "IN", "(SELECT DISTINCT MetaKey FROM [MetaMultiValueDictionary] MVD INNER JOIN [MetaDictionary] MD ON MVD.[MetaDictionaryId]=MD.[MetaDictionaryId] WHERE MD.[Value] LIKE 'some author')");
Hope this helps.
Nadya.