No widgets.  Looked in advanced settings and all other MusicCast settings and see nothing.  I should add that this happens when the preamp was powered on and then off.  The volume hijack occurs for an extended period after the preamp has been powered off and eventually the MusicCast slider will disappear from the phone.  I am not sure how long, but it usually takes overnight before this happens.  It seems as though the preamp stays active on the network for a period of time.