I like to use a Jackson guitar with an active mid-boost circuit straight into the amp. The extra mids help increase gain without going too muddy, and the tone controls (which are placed after the gain stages in Marshalls) can then be used to get the desired EQ. Many metal players boost the input of their amps with mid-heavy pickups and then use the tone controls for the scoop; Max Cavalera is a good example. Other than that, I don’t use any effects.
This sound is a rather fuzzy metal sound. If you use these settings with the tone shift disengaged it gets less fuzzy and is very articulate.
Tone Shift: on
Reverb: both channels as desired
Mode B: lead 2
Gain B: 8
Mode A: as desired
Gain A: as desired