I want to arrange a draft night for 6 players with tyrants expansion included.
What do i need to buy?
3 core sets and 3 of each booster?
One set of everything drafts up to 4 players. 2 sets of everything will get you to 6 no problem. But if you want to have only single copies of "red gem" cards to simulate rarity, I'm not sure how many complete sets you'd need.
EDIT: 2 sets is fine either way, even if you remove a single copy of all red gem cards from 2 complete sets w/Tyrants you get 296 total cards, easily enough to draft for 6.