Our approach to copyright is the standard approach for a fan project: hope the publisher doesn't complain. Maybe, just maybe it would be possible to get permission from Scholastic; do we have any business-major RAFians who have an idea how?
On topic, I'm not real warm on the idea of sound effects, they're more a technique of radio theater than audio books. The basic problem is that lots of text interferes with the flow of the sound effects, and sound effects interfere with the flow of text.
Another way to look at this incompatibility is to compare watching a movie to reading a book. When I read, my mental focus isn't on the language as much as the story. If the narration is good, it gets out of the way. In contrast, cinema or theater (including audio theater), the content is the story. There's very little if any narration, dialog is direct (no "he said" tags), sound effects and either visual presentation or unnatural dialog are used to convey action. ("'Did you see that?' 'He got hit by a train!' 'How tragic!'" Theater can get really silly.)
That said, KA makes use of a lot of onomatopoeia that could be cleanly replaced with sound-effects. ("Tzzaap"! "
Tseeeer", etc.)
Background sounds, I'm pretty sure, would only get in the way.