Cerison,
There's a good discussion of your question on this thread:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1149445567&read&keyw&zzzyx+silverSpencer,
I wouldn't say the copper sounds "better". Its transient response is faster and more lively/lifelike than the silver. I've heard this on multiple A/B ZYX comparisons. Whether you'd like one or the other is a matter of taste. (Of course I might have an opinion on whose taste is "better", but that's for another thread!) ;-)
Cheers,
Doug
P.S. Say "hi" to Raul for me next week, and for goodness sake make sure whoever meets him at the airport brings a warm coat, hat, muffler, mittens and a pint of brandy. The poor man's going to freeze. He was shivering here (CT) in December, and you remember how warm it was then.