Hi tconnelly.
Here's one of the posts that musiclover mentions.
Sampletank 2.5 - Omnisynth & Default DirectoryIn this post, there are instructions on how to successfully use Omnisynth as a general midi synth in Sampletank 2.5.
Also, further down the thread, this post explains about how to set the default path for Sampletank sounds.
Hope this helps,
Noel