Adobe Creative Suite 5.5 Master Collection and Production Premium editions include Adobe Audition CS5.5, which is a much more powerful audio editing application than was Adobe Soundbooth, included in previous versions.
After Effects CS5.5 includes an Edit In Adobe Audition command.
Chris and Trish Meyer provide a pair of video tutorials that show how to use Audition with After Effects:
Video2Brain provides a video overiew of how to use Audition to modify audio from After Effects.
For more information about using Audition with After Effects, see “Working with video applications” in the Audition CS5.5 Help document and “Editing audio in Adobe Audition” in the Adobe Premiere Pro Help document.
For complete details of what’s new and changed in After Effects CS5.5, see this page.