Nice site, something like that is my next project after I've migrated my clients site as above. Zak has kindly emailled me a workaround file to place into Preferences, but that hash;t resolved it for me - I will post a summary once I get to the bottom of this as I would;t want to speak on behalf of Zak just yet when he is working to resolve the issue - at least for the O2 issue.
Have you checked any assets that have become unlinked?
PS i wrote the in-race music for Slingshot Racing on iOS and Android, which has asynchronous play, so nice to see what you are doing too.