If I understand you question,you want to harmonize.Just do whats musically relative to the other guitarist.If hes playing around the 8th fret,you could do what hes doing an octave up or down e.c.t.change some notes here and there so mabey its slightly different than what hes playing.Theres lots of ways to harmonize...experiment with it.

To get a good CLASSIC metal tone,then just set the bass midway,the mids high,and the highs midway...tweak as needed.Adjust your gain until your ideal crunch is met.