I just switched from a solid core silver digital coax to the Tributaries one in my sig (stranded silver plate copper), and it may be due to other factors like the shielding, connectors, true 75 ohm impedance or whatever, but I like them better. I can't really speak as to the "sound" of them, but there's more weight and detail with the Tribs.
Speaking of buffers, wavoman, I'm using these Tribs between my CDP and a Monarchy DIP, and from there to my DAC, and I'm really happy with the whole combo. The DIP reclocks and boosts the output signal feeding the DAC, and there's been a big improvement in the overall sound character - more detail, heft, and imaging. Really happy with it overall now.
With an analog IC, I think there are a lot of factors besides conductor material that play into the sound of them - build, shielding, geometry, connectors, etc. I've tried both well shielded but fairly cheap Monster copper ICs (and others) and the ones I'm using now (Signal Cable Silver Resolution with Eichmann plugs), and the Monsters had a more muddy, smeary sound to them...not like it was REALLY bad, just not as nice as the silver. THe silver seems more resolving and detailed, like more of the music is making it to the amp. IMO, a lot of the "brightness" attributed to silver is due to the well defined higher frequencies...there's better transmission, but like I said, there's a lot of factors in cable design that can effect that.