Only one of the CS series can be installed and active on a single computer.
Where did you hear that? That's simply completely untrue. Using multiple versions of CS products never has been an issue and neither is it for CC and CS6. Each major version uses it's own unique activation.
It happened to me a few years ago. When I tried to install the then latest CS version while the previous version was installed and active, the installation software told me to remove the previous version.