The result of a few hours of hacking:

pavucontrol cannot only control the volume of hardware devices of the Polypaudio sound server but also of all playback streams seperately, much like the new Windows Vista volume control application.

Get the Polypaudio Volume Control while it is hot.

On a side note I released updated versions of both the Polypaudio Volume Meter and the Polypaudio Manager which are compatible with Polypaudio 0.8.