Metallica was king of big guitar sounds. They were the first to make it sound REALLY BIG! They used like 8 marshall 4x12, with various mics and a huge tent cover to enclose the sound. The guitar sound you hear on the black album is clean, crisp and dint require a whole lot of dubbing. I think the best way to do it, is to put a condenser mic somewhere in the room while putting something like the sm57 a little off the cone of the cab...mix the two mics until you get the perfect sound.