YOu need to go to a K8 to get a silencio WBC. At K6 level its WBO or Silencio, but not both.
They are a lot better than the standard grinders and yes, they need to be ordered. I dont see them as significantly quieter than a Macap M4D for example. I am going to make a demo out of one on Saturday morning if youd like a listen.
Try some white noise with the bub. Its been a godsend with ours.