There is a discussion here
https://www.mobileread.com/forums/sho...d.php?t=190338
The features are described on the Amazon site:
http://www.amazon.com/b/ref=amb_link...d_i=1000827761
It would seem to be connected to Audible where you can switch between audible version of the text and reading version of the text and keep your place in both versions. It does not seem to be simultaneous. You have to own both versions.
Dale
Dale