Our group would sometimes have that problem. One way I'd try to keep the adds from getting out of hand would be to have the 6th person who covers ogres, focus on them from Inside the Aura of Immortality just as Oryx is staggered the first time. If I'm on ogre duty, grenades and an LMG would quickly dispatch them in time to continue putting damage on Oryx with the relic holder, just as the rest of the team was returning from bombs.