First of all, mixing copper and silver is fine and in fact quite common. The vast majority of cables made have brass ends with gold plating, and brass is a much poorer conductor than copper or silver.
As far as the speaker wire to IC conversion, yes it's possible. You'll likely have a hard time fitting the wire into your RCA connector, but you can make it work. You'll probably have an easier time and a better sounding cable if you just try to make one from scratch.
As far as the speaker wire to IC conversion, yes it's possible. You'll likely have a hard time fitting the wire into your RCA connector, but you can make it work. You'll probably have an easier time and a better sounding cable if you just try to make one from scratch.