Welcome to the boards. You definitely came to the right place for help - there's a ton of cats on here with decades and decades of combined knowledge.
I used to run a Marshall/Boss/Ibanez combo and swore by it (that's what I'm running in my avatar pic, actually - granted it's a JCM900 full stack). If you get the opportunity, I'd swap the Metalzone for an SD-1 or OD-2, both seem to play nicer with Marshalls than the MT-2. Another thing to consider is the pickups. If they're stock INF pickups they're going to sound thin no matter what you do. By just replacing the bridge one with a Duncan Distortion or Dimarzio Super Distortion (or better yet, an Elysian Hades Trident II ceramic bridge pickup) you'll hear a huge difference.
What used to work for me was to barely crank the amp gain and drive it with the OD2. I found trying to push the amp's gain then piling on more from the pedal just made it sound fizzy/soft. But, keep trying, I totally understand how the tone you get either inspires or de-motivates, but you'll get there.