If you can get Python to write a command line like this:
open "file://localhost/Volumes/Macintosh HD/yourSounds.kym”
Mac OS is supposed to open the document in the default application for its type (as determined by LaunchServices).
A better solution would be to open your Tool (a file with the .pci extension), rather than a Sound file. That will start the Tool (and your Tool can play the Sounds).
To silence the startup Sound, you have to edit the Preferences>Performance. Uncheck "Play sound when DSP initialized".
Kyma will start with the same windows open that were open the last time you quit. So if you quit with most of the windows closed, that should prevent too many of them from being open when you launch the Tool.