Comment 12 for bug 1359249

same as #1443229.

I investigate the source code of indicator-sound, and find that in src/service.vala:

var env = Environment.get_variable ("DESKTOP_SESSION");
string cmd;
if (env == "xubuntu" || env == "ubuntustudio")
 cmd = "pavucontrol";
else

I think you would support more desktop environment such as XFCE by adding " || env == "xfce""