Got it, however I’m still having problems.
I went ahead and upgraded to Dorico 3, I was planning on doing it anyway. I downloaded the “Dorico Pro 3 Sounds Installer”, and unpacked everything (I think). However, in the Library Manager I have my Cubase and Padshop content, but no Dorico content. When I open a new project in Dorico or apply the HSSE+HSO template to an existing project, HSSE is loaded but all the channels are empty.
Inside the installer folder I see an installer for HSSE but not HSO. I’m still pretty confused.