After one player spent a few nights playing the game solitaire (and having astaroth repeatedly destroy the world) and reading up on strategy, we tackled the game again, this time both knowing HOW to win and having a couple of fake player-characters who we used to farm items. More players does mean more monsters, but carefully choosing party skills to maximise getting all the cool loot early in the game meant that we could generally handle the monsters. This time, we won without too much trouble, and it took less than three hours.
I feel like we cheated, somehow. Other player says, "It's not cheating to go straight to where the items that make you win the game are and get the items that make you win the game, that's more appropriately called 'playing'."