I play all sorts of metal and my current set up is this ...
Jackson Kelly w/ EMG 81/85
Earnie Ball strings (the ones w/the thicker lower strings)
Tuned 2.5 steps down
Marshall TSL 60 w/the cheap cab (had to cut some corner) from the MG series.
First off, tube amps are meant to be played loud. You can get cool old school death sound by dropping the presence and treble to around 5 - 6 and keep the bass full and the mids around 3 -4. Increasing the treble and presense makes it sound sharper. Usually as the volume goes up, bring the presense back a little. I can get the sounds I want from Metallica, to Nile to Bolt Thrower.
Pantera, Slayer, Meshuggah, Metallica, Necrophagist, Vehemence, Killswitch Engage, Nile, Dying Fetus, Opeth, Dimension Zero, The Haunted, The Forsaken, Anata, Grimfist, Lacuna Coil, Ayreon, Carcass, Imperanon, Children of Bodom, Hate Eternal, Bolt Thrower, In Flames, Soilwork, Arch Enemy, Carnal Forge, Nevermore, Hypocrisy, Decapitated, Suffocation, God Forbid, Divine Empire, Fear Factory, Machine Head, Damage Plan, Black Label Society, Lamb of God, Death, BOOM!