I had the opportunity to buy a used Kurzweil PC2 module in December from a member of a German forum, with the orchestral expansion included. I was so close to buying it, the owner was quite annoyed when I eventually cancelled it.
The Kurzweil owners have told me that most of the symphonic sounds are still identical to the PC2 series. The strings just have additional articulations. Of course, if you add the KORE expansion, there are new brass sounds etc.
In the end I just didn't have a very good feeling considering that the entire orchestral expansion has an incredibly tiny waveROM of 16 MB. It does sound quite realistic, I checked demos over and over, but I also found some opinions saying that the Roland SRX 04 strings are a bit more realistic. I decided that probably the difference between the best of Integra symphonic sounds and this Kurzweil expansion are too small to justify purchasing a rack that could be 15 years old and soon have some defects.