http://forum.audiogon.com/cgi-bin/fr.pl?ymisc&1217698518&readThere are some good comments from several members in this thread.
If you have any experience with German cars, I would characterize the
Siemens CCa as Porsche 911, and Amperex PW 6922 as BMW 540i. Both are fast and precise. The BMW has a certain suppleness that ever-so-slightly smooths rough roads while still providing the driver with excellent road response, while the Porsche transmits the road surface untouched.
Both tubes create very a large image size IMO, larger than any other tube in
the 6DJ8/6922/7308 family, and each takes treble response right up to the
line of being "too much of a good thing" without crossing over the edge. It's
this treble extension that provides the outstanding spatial cues. I believe the
CCa can be too exacting at times, whereas the Amperex are generally more
forgiving...but this is just my opinion in my system.