both FDR/CVR ended their recording at the same time without indication of trouble. This means that both systems were damaged simultaneously, a very unlikely event in case of canon fire, but fitting the case of a missile hit.
The two recorders stopped because of lack of power, not because of other damage.
Power to the recorders comes via the Main Equipment Bay which is located below and behind the flight-deck. MEB remnants were seen in the same wreckage cluster as the flight-deck indicating they separated at the same time.
I totally disagree with the theory it was cannon fire, but at the same time, you can't claim simultaneous cutoff of recorders proves this. All that's required is the MEB is catastrophically damaged. This can (did) result from in-flight breakup of the front section from whatever cause.