I'm not sure at this point. The final version of the ebook is not quite finished. When it's done we'll do a deep comparison between the posts we've previously recorded and the posts included in the ebook. If the post hasn't been changed for the ebook and the flow of the reading isn't broken by using a previously recorded version then we'll re-use the original audio, otherwise we'll record a fresh copy.
LessWrong is getting ready to release an actual book that covers most of the material found in the Sequences.
There have been a few posts about it in the past, here are two: the title debate, content optimization.
We've been asked if we'd like to produce the audiobook version and the answer is yes. This is a large undertaking. The finished product will probably be over 35 hours of audio.
To help mitigate our risk we've decided to Kickstarter the audiobook. This basically allows us to pre-sell it so we're not stuck with a large production cost and no revenue.
The kickstarter campaign is here: https://www.kickstarter.com/projects/1267969302/lesswrong-the-sequences-audiobook
If you haven't heard of us before we've already produced some sequences into audiobooks. You can see them and listen to samples which are indicative of the audio quality here.