It is usually recommended to do timing and stuff in an editing program before you start work in After Effects. AE's not really built for real-time playback. However, there are a number of good ways to preview sound in AE. During a preview you can even place markers. Here's some info. (I know it's from CS5, but all the same stuff applies.)
- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')
No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.