I think the easiest way for you to fix that would be to allow having sounds in multiple formats, and it depends on the browser which one is (pre)loaded/played. (Easiest would be to allow multiple uploads. Even better would be to upload WAV or anything we want to, and PlayCanvas automatically converts them into the best formats for each platform.)
We’re currently in the same situation as lapinchatware. We can’t use WAV because they’re too big, we can’t use MP3 because they don’t loop seamlessly, and we can’t use OGG or AAC (not sure if AAC loops seamlessly though) because they’re not supported in Safari or Firefox respectively.
In the end we use WAV, even though it means that sound loading times are abyssmal.