Prepare or un-prepare an event asynchronously. The events are identified by string (refer to 概説 for a discussion on using strings and IDs). The event definitions must already exist in the sound engine by having explicitly loaded the bank(s) that contain them (with LoadBank()). A request is posted to the Bank Manager consumer thread. It will resolve all dependencies needed to successfully post the events specified, and load the required banks, if applicable. The function returns immediately. Use a callback to be notified when the request has finished being processed.