the only things I can think of that could cause a 9,000 fpm decent are a spin or inflight airframe breakup.
Spins usually don't have such a high rate of descent unless they turn into a spiral dive. Spins are characteristically quite flat. Having said that I have never flown an RV6.
But in other light aircraft I have flown a fully developed spin usually sees ROD around 3,000 fpm. It will be interesting to see if the whole empennage was intact up to the point of contact with terrain. There was some story about part of the aircraft falling hundreds of metres from the main debris field. Was that ever proven? What was the debris?