i also have a metal zone, and for nice, heavy stuff, i've not really considered much else. i also have a marshall guv'nor, which has an amazing marshall sound out of vintage fenders (you just have to try the combo to believe it). if your amp is solid-state and you want some serious tube growl (or tube and you just want to sound huge), try
the mesa-boogie v-twin. i was astonished with the immenseness of the sound on the one i ran through a bassman, and it could sure beef up an overly bright amp. personally, for heavy music, i go with my explorer through a metal zone with bass and treble cranked, mid freq most of the way down with the mid level at about 9 o clock, running through
an alesis microeq with bass up full at about 75hz with q=2 octaves (q is the band size, right? i'm kind of an amateur
, middle set at ~510, most of the way down, q=2 octave (choice on this pedal is 1/2 octave or 2 octave range), treble at about 2.5k at 9oclock for level. i run this into a silverface ('70, i think) fender
musicmaster, a very simple amp that is designed to work well with bass or guitar (like a baby bassman combo kindof). with the q buttons on my microeq and the pickup selector and tone knob on my explorer, i get a staggering range of great heavy sounds. my usual sound is kind of static-x/system of a down/tool-esque. really deep, monstrous, immense sustain,and (assumedly becuase of the treble cut on the microeq), almost gated-sounding. very nice signal-to noise, though the self-noise on the metal zone can be a little high the way i have it set. (maybe i should cut treble on it and up it on the microeq-hmm). in any case, it's the monster tone for me, suitable for many heavy sounds. i can even kill the metalzone and run my acoustic in for a great bottom-heavy, punchy days of the newesque tone. your mileage may vary, of course, but for a reasonably low gear budget and no need for a huge amp because i'm mostly just recording, it's phenomenal.