I have a large cookbook collection with almost half a million recipes on my Bookshelf. The two ways I deal with large recipe search results is to sort the results by Buzz so I see the recipes that most other members have engaged with. Or apply my bookmark filter "I want to cook this" to see recipes I have already identified as being of interest.
In terms of searching within groups of books, I suggest creating and adding bookmark tags with whatever your needs are. So for Indio32 that would be European, Asian, Nordic, etc. Then when recipe searching they can apply that bookmark filter to say only see recipes in say their Asian books. Of course they can also apply the EYB Asian filter to just see those recipes so that's not the best illustration. But your bookmark filters for your books could be Complicated or Easy, Weeknight or Entertaining, Winter or Summer, Favorites or Unloved - whatever works for you.