My book is with ACX - Can I use Findaway Voices to get to Apple Books?

Yes - if your book is non-exclusive with ACX.
 
Ultimately, if titles go to Apple Books from multiple distributors (e.g. Findaway Voices and ACX) then Apple will make the decision for which titles to make available for sale. The great news is we have a very deep relationship with the Apple Books team and are featured on their short list of preferred audiobook providers (https://itunespartner.apple.com/en/books/partnersearch).
 
We are working hard to ensure Findaway Voices titles, with the royalty of 45% of DLP, will be prioritized as the versions that are made available on Apple Books and have already verified that our versions are currently being added to Apple Books.