Well the soundboards started as the mp3s rippable off the website which is unfortunately the best we have so far (I'm no audiophile though. They sound totally fine to me).
The sounds from the book were recorded with a male to male audio cable, one end in the sound module, the other in the 'line-in' jack of my mac. So that's as raw as you're gonna get without opening up the module, working out what kind of flash memory it uses and doing some hacking/soldering. And even then, it might not be a standard audio format, but something specific for the hardware.
The reason I've suggested 48khz 24 bit is that it's apparently preferred for a Final Cut Pro project (and one can assume in other programs too). It accepts 44.1khz, 16 bit of course, so I don't know what the benefits are in practice.