If you want a CONSTANT speed (i.e. not gradually slow down or speed up) you can simply hold down the CTRL key as you resize the clip. The audio will follow. This method will allow speed changes from .25% to 400%.
Velocity envelopes will let you run in reverse or use varying speeds. They only work on the video track.
Ctrl-Stretch/Squish maintain sync between the audio & video, but won't allow reverse or varying speeds.
If you just want both to run in reverse, use a velocity envelope at -100% on the video track and export the audio track to something like Sound Forge to reverse it.