These plugs make no difference whatsoever. There is no technical reason why they should. Inputs do not radiate, so no reason to put caps on them. If they pick-up stray noise, then it is a bad design.
The only REAL plug that is effective would be for a coax or AES/EBU output. This would be a 75 ohm or 110 ohm terminator plug. This will terminate the output and prevent spurious emissions. Even the value of this is questionable. Waste of money IMO.
Steve N.
Empirical Audio