If they are 6-9 per box, that means they have about the same rarity of a normal holo. Think about it. There are 34 rares, so you will get almost all of the rares. And if you get 6-9 primes you will probably get all of them also. So its like each rare is 1 per box, and each prime is 1-1.5 per box.
So as a pokemon community, we should stick it to the man and value prime cards just like normal holos.