There's something I don't understand about the CVR. It says this runs for two hours and then starts from the beginning and overwrites what's on it.
According to the report, it sounds like the QF30 had the newer type digital recorder with 120 minutes of recording (although some of the 744's may still have the older 30~40 minute tape type).
The erasure process doesn't wipe out the entire 2 hours. The tape or memory will always have the last 2 hours of the flight on it (or 30 minutes). CVR's on Qantas' 744's are operational
whenever there is power on the #3 AC Bus.
If the CVR circuit breaker was not pulled and power remained on the aircraft after landing, then the CVR would have continued running ... and the explosive event would have been overwritten.