An answer to "why Kirsty opened the box"

People keep asking this question, I think it's pretty simple. She KNEW she could make a deal with Pinhead as she'd done it before. He cheated on her numerous times and she wanted him to suffer. Not just die. Not just go away. She wanted him to feel pain.

So it's quite simple really. Hell hath no fury like a woman scorned. I think that was the general thesis of this entire movie.

By the way, I am right behind you.