As AndrewB said, you will need to do an upgrade of the existing EV site. You can't just point an EV 9 installation to an EV Directory db and have it convert it.
I have 7.5 and want to do an in-place upgrade to 8, then to 9, then move 9 to a 64bit platform. I know that I have to sequentially upgrade but i have a few specific questions.
a) is this upgrade approach correct and reasonable (understanding that there are pot intall tasks that must be done with each)
b) do i need to upgrade all the prerequisites for 8 before upgrading to 9, then upgrade prereqs again for 9 before moving to 9?
c) are there "data migration" steps i must follow as i move up in EV versions, or just at the end when i reach 9 on 64bit?
Thanks in advance for your time and expertise!
Thats only true if you are migrating from an old site to a new site.
But unless i'm misunderstanding things, you are just simply migrating EV to new hardware? in which case moving vault stores and index volumes is pretty simple and doesn't require any 3rd party add ons
How to move indexing locations to a different EV Server in the same site:
How to move a vault store to a different EV Server in the same site:
And the slightly more over the top "How to move EV to a new server"