Have you checked at  https://www.closed-circle.net/  This is CJ's and Jane's collaboration with Lynn Abbey on their own books.  If you would like to communicate directly with CJ, here is her blog: https://www.cherryh.com/WaveWithoutAShore/  She puts out a lot of information there, and you might find your answers, or she might be able to directly respond to your question.  I have no idea who publishes the audio books, so can't help you there, but maybe the links will point you in the right direction.
 

No luck at Closed Circle. 

Unhappily, I have a problem with access to Wave Without a Shore.  I established a login many years ago with an email that's no longer available and of course I don't know the password to that account.  I tried an updated username, but for some reason never got an acknowledgment email, and now both my preferred username and numbered versions of it as well as my current email come back as "already registered" and yet no luck with "forgot my password." Sigh. I'm not really sure how to correct - probably quite a mess with the attempted accounts.

I was told today by an audiobook retailer that both the books are on the publisher's release list but that specific dates have not been given. So, apparently  Resurgence and Divergence ARE coming but when is up in the air.  Hope springs eternal, as they say.

The idea of a dramatizarion of Downbelow Station has made me breathless with gleeful greedy anticipation! Surtac, please say more about that!