Shorting plugs....

My father has the AR Ref3 and I ws thinking about these for him, he is going balanced to amps and from CD player but capping the empty jacks still strikes me as curious and a nice stocking stuffer.

You'll actually improve the sound of your system if you unplug all components from your preamp other than the one you are using at any one time (even if the other components are not turned on). This eliminates rf from the unused components.

More than a thought. More even than a feeling. I do this in my system, because the improvement is material.

Concur with Chadlinz, it's an impractical "solution" and just because "the improvement is material" *in your system* does not mean that it will be in anyone else's system.

Also, when you indicate that you turned off components, what does that mean, did you unplug the components, turn off power at the wall or simply press the power off switch on the components?