Shorting plugs....

With Pass Labs stuff you should use the balanced inputs/outputs when possible anyway.

I tried the shorting plugs on my preamps unused inputs and I really cant tell any difference.
But, what the hey, they are really inexpensive and I already had them.

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.

Thats one school of thought, its impractical and many times next to impossible and inconveient but its a thought.

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