I don’t know for sure. =) I have been looking up the books mostly from SCM recommended lists, my bookcases, favorite authors, AO, a recommendation from someone on this forum…just whatever.
I guess sometimes it’s based on whatever I am interested in at the moment. When I print a booklist I often take the time to quickly check them against the libivox catalog. I have a dd that learns much better with audio and a book together, so we use them as often as I can so I can be free to do something besides read out loud all day. =)
I have found several of the Burgess books as audios since we love them:
http://librivox.org/the-adventures-of-buster-bear-by-thornton-w-burgess/ which is a 106 Days of Creation book
and there are many more:
https://catalog.librivox.org/search.php?title=&author=Thornton+Burgess&status=all&action=Search
Jane Austen:
https://catalog.librivox.org/search.php?title=&author=Jane+Austen&status=all&action=Search Pride and Prejudice, Emma, more
Louisa May Alcott:
https://catalog.librivox.org/search.php?title=&author=Louisa+May+Alcott&status=all&action=Search Little Women, Little Men, Jo’s Boys and more
Shakespeare – I love this! Most are his actual plays. We read along in our books as we listen if I don’t have a good BBC movie version:
https://catalog.librivox.org/search.php?title=&author=Shakespeare&status=all&action=Search
Anne of Green Gables series:
https://catalog.librivox.org/search.php?title=&author=Lucy+Maud+Montgomery&status=all&action=Search
Lots of the Yesterday’s Classics and several of the Heritage History’s collections are on there. I did a blog post about the YC collections that were on audio through Librivox here:
http://mysouldothdelight.wordpress.com/2013/02/27/yesterdays-classics-ancient-greece-books-librivox-audio-books/