In Premiere Pro, you can edit audio, add effects to it, and mix as many tracks of audio in a sequence as your computer system can handle. Tracks can contain mono, stereo, or 5.1 surround channels.
In Premiere Pro CS5.5, and earlier, it is important to add the proper kind of audio track for editing your media the Timeline: mono, stereo, and 5.1 surround.
In Premiere Pro CS6, audio tracks have changed significantly to allow for any kind of audio format. In addition to mono, and 5.1 surround audio tracks, there are now standard tracks, and adaptive tracks. Stereo tracks have been removed.