I already have sound enhancement when I read ebooks - it's called "the-TV-is-on-in-the-same-room".
I mean, really now. The whole point of reading is to exercise your imagination, not to have it spoon-fed to you. If you want an audiobook experience, buy an audiobook.
Can you just imagine the horror of reading one of Laurell K. Hamilton's Anita Blake books (post-
Obsidian Butterfly) with sound enhancement??? I shudder at the thought of how LKH (and others) would run with that concept.