No, different editions between Preferred and Advanced. Descriptions of each are in the knowledgebase. I recently upgraded a customer from 8 to 8.1. I talked to our tech support and they said all I needed was the large upgrade licence since, just as your situation, the customer had Preferred and Advanced but no Essential Edition license. What the system did is created a Virtual Essential Edition License. But as tlPeter informed us in the thread I linked, if your cabinet dies so does the Virtual License.