I must agree that Metal Zone is probably the best distortion pedal myself, or any other musician I know, has seen or even used.
But as far as the perfect tone goes..............I don't think it's just guitars you're hearing on the album. The bass and the guitars are occupying alot of the same frequencies, thus lending some of each other qualities to the overall tone that you are hearing on the album. Besides..it's an album, they spent hours upon on getting the sound just right and then EQ'd it all to hell. But the album does sound great...fucking great!