OK, I hacked away at this until I finally figured it out. There were two issues.
1) The Toontrack Read Me file instructs installing the 32 bit version for use with 32 bit hosts. I have Studio One Artist which, I understood to be a 32 bit host. Going to the 64 bit EZKeys was the first step to getting this running.
2) The EZKeys software that I downloaded was not up to date and had to be updated to the latest version to work with Studio One.
In summary: Make sure to install 64 bit Toontrack software for use with Studio One Artist and check for updates.
I hope this can be helpful to someone else. Thanks for your answer, Alex Tinsley.