I've been building pure silver speaker cables and power cords for years from three-nines soft-annealed round wire or flat wire sourced from Rio Grande. The key to avoiding stridency is soft-annealing. A wise manufacturer of 4-nines silver wire once shared with me that 4-nines or higher is largely a marketing gimmick.
Pure Silver Wire
If silver is so good to use why do we not see solid silver speaker cables? Price is not that high- 10ga diameter pure silver 6ft is just under $300. That makes a pair of speaker cables about $1,100 for material. I see the price of some of these cables on the market and $1,100 is a fraction of their asking price.