Hello,
Unfortunately this is a known problem with Safari, which consecutive releases of PennController try to address with more or less (emphasis on less) success…
I’ll try to rethink the preloading method again for the next release, but in the meantime you should definitely package your audio files in one or several zip archives—you shouldn’t have any problem with that since you’re already hosting your resources on a dedicated server. Follow this guide for instructions, and don’t hesitate to ask any questions you might have
Jeremy