I don't want to get bogged down in definitions here, but I don't see how you can call them audio books. An audio book is a book or written fiction which is read, like this or this or these. Full cast versions of these are here, here and here where the parts for the narrator and the different characters are read by different Voice Actors (VAs).More often then not they sound like the TV is on in the next room and I'm listening to the episode but not watching it.
That isn't radio theater, it's more a full cast audiobook with sound effects and a score.
The defining factor here are not the production values, the content or even the use of a narrator, I believe it is a production decision - how are you communicating your story?
If you are giving the listener a dramatisation, a "movie without the video track" as I've heard it called one time, the script needs to be tailored to that. You need to give audio clues to the location, the people present, the facial expressions, the moods and all the other hundred-and-one things that your audience would normally see. This is why they call it the cinema of the mind - the audioscape (did I make that word up?) that you give the listener with which they construct the scene in their mind's eye.
If on the other hand you are storytelling then you are in effect taking the place of the internal voice which we all hear when we read a book. Depending on which book I read my internal voice can be James Earl Jones or Maggie Smith, I spare no expense! Its not just a matter of storyline exposition or painting verbal pictures of the scene, the job of a narrator in an audiobook involves subtle communication of the emotions of the actors, God-mode insights that none of the characters know, ultimately it involves creating a feeling in the listener that matches the tale you are trying to tell. The narration I used in Tales of Death And Honour would be totally unsuitable for a Laurel K. Hamilton supernatural sex thriller LOL!
Here you have a very valid point with regards to something that turns off mainstream listeners - large casts are hard to follow. Large casts are only viable when each member has a unique verbal signature that is instantly reconisable and their part, their back-story, is either simple or well established. I think you have some excellent advise with regards to building up the complexity of the drama....I know you guys have a fairly large cast over there and while that works for a video where scene changes are more obvious I think it's a liability for audio.
Take a listen to Mark Yoskimoto Nemkoff's Shadow Falls season 1 and I think you'll hear what I mean.
http://shadowfalls.mevio.com/#show-episodes
When this first came out, I thought it was fantastic, now after studying old time radio I want to strangle him. Too many plotlines, scene changes that will have you wondering who's talking now and a large cast with such convoluted back-stories that you'd need trading cards to keep track of them all. And that's just episode 1!
Had a quick listen to Shadow Falls and it is an audio book, well delivered to be sure but obviously others have mentioned the difficulty in following all the convolutions since he has periodic "companion" pieces - not a bad idea.
Good luck! Push the envelope!!!I am working on getting some of my audio ready to release and hopefully will get off my dead arse soon.
K