I think my response is a little simplistic.
The cabinet is bigger and there is more "magic gook" (the stuff that makes it sound good) inside.
And let's not forget the cryoed premium outlets.
The value of the 4, 6, 8 is that you don't have to purchase more power cords that would be required by 2, 3, 4 Hydra 2s.
As always, tailor your perspective to read:
"I'm not buying equipment, I'm buying GREAT SOUND!".
Makes spending the big-bucks easier...