Q2: What about metals—copper versus silver versus gold versus what? How about blends?
Silver is the fastest conductivity metal (IACS 105%) in the world and it has lower resistance , (Silver 16 < Copper 17 < Gold 22 nOhm-m), so that it is often used in high end interconnect cable to give a rapid signerl transfer . It is also widely used in high end speaker cable and power cable, but as the sizes are much larger, the prices very.
Copper is the 2nd conductivity metal(IACS 100%)and then Gold 3rd(IACS 80%).
Generally , Silver helps to produce a faster treble sound , copper improves the bass , and gold is more widely used in Connector plating as it won't oxygenate . OFC(Oxygen Free Copper) or TC(Tinned Copper) are the basic entry level budget conductors; some expensive materials are often used in audio cable , such as SPC(Silver Plated Copper, 4 times more expensive than OFC) , OCC(6N purity copper, 6 times higher than OFC), Pure Silver(200timeshigher than OFC) ; along with many others conductors that also can be utilized.
Blending/Mixing different conductors :
Different metals can be deigned in to conductor aggregating ,and this is more common in Speaker cable or Power cable because more copper wire used ; such as mixing OFC & SPC is designed to balance the treble and the bass.
But it is difficult to define what is better between mixing or non-mixing conductors , many other designs details can give a greater or smaller result .