They could make DOAX a great game if they kept with the wacky focus and made the volleyball more action packed. But yes DOA6 first. They probably can do them both at the same time.
A DOAX game that made the volleyball more like Beach Spikers or Outlaw Volleyball would be perfect. Throw in a fighting mode on a couple of beach stages and you have something worth playing, but yeah- just make volleyball a mini game.