Wave Editor introduces the concept of "Layers" to audio editing (patent pending). Layer portions of audio of any format, channel count, sample rate and bit depth, Audio Units and fades on top of each other, edit to your heart's content, then "flatten" your file to get a result that would have taken much longer the old-fashioned way!
Audiofile Engineering Wave Editor v1.5.6 MAC OSX-UNION
Wave Editor is THE audio editor for Mac OS X. Designed in Cocoa from the ground up, Wave Editor proudly takes advantage of Core Audio, Quartz, and other solid OS X features.