Silver solder is only 4% silver, the rest is tin. You can pay more for it, but it is still 96/4 when you are done fishing out the money for it.
The problem with silver solder is it melts at a much higher temperature, so it is more likely to ruin something that is heat sensitive. Also, it is harder to get a good solder joint and that will affect sound far more than what alloy you solder with. It also requires a more active flux to flow properly and that is usually not good for electronics. But, for binding posts, it probably won't matter which flux you use.
Silver solder was made for plumbing, as the lead content will get into your water and that is not a good thing. 60/40 lead tin or 40/60 lead tin with a rosin flux is the most ideal solder for electronics you can buy. If you want to get fancy, go for it, just understand it is far easier to ruin something than improve it. So be careful when you use the higher temperature solders.
Here is a alternate viewpoint: A lot of years ago, I worked in space and missle hardware. NASA uses lead tin alloy as it was the most reliable and dependable joint you can make. Believe me, they could afford silver solder but it was banned. I am not sure what they are using now with all the lead free requirements floating around these days.