As a cable manufacturer, My experience tells me that cable geometry is a bigger determinant of perceived brightness, which is a way of agreeing with you Rockitman, but with different words.
However, copper and silver have different characteristic sounds with copper adding a thickness to the upper bass and lower mids, which tends to make the sound warmer but muddier than silver. If you design a cable that sounds balanced with copper, and substitute silver, the muddy accentuation of mid-low frequencies goes away and the silver introduces it own resonant problems in the lower treble. The resulting cable may sound too lean and bright.
The challenges for a cable designer are therefore quite different when using copper than when using silver, and a reasonably balanced result is possible with both of them.
My company never uses copper as copper cannot achieve as low a noise floor as silver or gold. What we do find is that there are several ways of combining different metals (in our case silver, gold and platinum) that can significantly diminish the characteristic sounds of the individual metals. Many others still get excellent results by just using geometry to balance out the characteristic sound of the metals. It is all in the implementation, and judging cables by the metal used is mostly meaningless.
