Charles1dad,
I agree. The Cast Cu are an exceptional cap. I mentioned Ag because the question was asked concerning the silver.
The question I did not answer was will Cast Cu mate well with Ag wire. That depends on the silver wire. I have never used dc10audio silver wire so I have no comment.
Mountain-high,
I went to dc10audio website and read that they design their speakers like musical instruments. To the point that they use tonewood. They believe in a resonating speaker box but choose, as their top cap choice, a Duelund Cast that has been designed to do the opposite. Staying with the theme of material used (tonewood) for musical instruments, the Duelunds uses the metal (copper and silver alloy) of musical instruments. It seems odd they did not choose a cap that resonated to go along with their speaker.
I'm not deliberately trying to be antagonistic. The two seem contrary to one another and from my experience this is where you start to throw more money into a system than what is needed.