I tried using silver solder, which I had never used, and my cheapo soldering iron wasn't hot enough to melt it. I ended up using regular solder. I got the silver solder from my wife who just learned to do silversmith work. She uses a small torch. That's what silversmiths use. I didn't think a torch would work very well near the crossover board.
I replaced the caps on my 1984 Klipsch KG4s with sonicaps and WOW, what a difference. It's like buying new speakers! I learned about sonicaps from Danny after building a pair of AV3s. Love them.