After two computers and 3 different Windows versions since X1, I discovered that I had not re-installed all of these additional bundled sounds for Dim Pro. Other than the Dim Pro Expansion packs, these do not appear to have shipped with Sonar since X1 Producer.
The additional content for Sonar is often loops, or demos, etc, but in this case there is 1+ GB of samples for Dim Pro. The Classic Keys are really good!
The file name from my X1 downloads is
05_SONAR_X1_Producer_Additional_Content.exe