USB Audio Problem with Dell LT and replicator. - Sa

I have a Vista Enterprise laptop (Dell) connected to a Kennsington model
33232 USB port replicator.  Everything seems to work fine (network, printing,
mouse, etc) except for the speakers.  When I go to control panel-->Hardware
and sound-->Manage Audio Devices-->Select USB speakers (shows working) and
click on properties and then click on the level tab.  I cannot move the
volume control slider.   I can move the line-in and microphone sliders.

If I connect an XP machine to the same device, sound works great.  Any ideas?