Hello,
Sorry to hear you are having issues. But, if you purchased SoundPackager from Steam. You should only download and activate it via Steam. You should not use the installer from Stardock, since this version will ask for Stardock's Sound Packager key to activate it and you don't have those.
You just need to run you Steam->login->Library->SoundPackager->Click on "Install"(Blue Box)->Once that is done, the installation and activation will take place. You don't need Steam to be running in the background for SoundPackage to work once it get activated.

Thank you.
Basj,
Stardock Community Assistant.