Just installed some Zaffiro strings by Aquila and they sound good. They are advertised as being as close to the sound of carbon strings without being carbon. This sounds about right to me, the trebles seem to be a bit louder than any nylon strings I have tried, and brighter than most nylons. This works for me, since I have a spruce top guitar that needs help in this area. What I don't like about carbon strings is the thinness of the sound, and the thinness and high tension of the strings, but they do have a bright and loud sounding quality.
The Zaffiro seem to intonate well, and so far, sounding very good. Bass strings are the supernylgut.
I think they are a good alternative to carbon strings.