You can have them both installed, and as it turns out, they do both run at the same time.
But Dynamic Link is between same versions only.
Thank you again Mr. Simon.
What Jim said... AND do not delete CS6 if you intend to use Encore for DVD or BluRay
CS6 is the final Encore http://www.adobe.com/products/encore/faq.html
-Cloud and Encore http://forums.adobe.com/thread/1236852
-a workaround for the Cloud http://blogs.adobe.com/davtechtable/