Cables to Add Brightness

I was just wondering which cables will bring the largest impact in adding brightness to the upper midrange and treble? Power cord, interconnects (XLR) or speaker cables.

Next, any recommendations? I am aware that silver plated copper or solid silver tend to do better than all copper. If this is true, what are the brightest sounding cables you have tried which managed to add more sparkle and treble extension to your system?

By the way, I am referring to all the good aspects of brightness ie. sweet, airy, 3-dimensional, tube-like glow and extended treble.

Not negative aspects of brightness such as brittle, hard, glassy or distorted type of treble which sounds like tin can.

I would appreciate any thoughts or experience.