It is my primary source of gain, what else do I need with it? I basically play Norsecore/Melodic Black Metal, Technical/American/Old School Death Metal and Thrash, and varying solos of shred, etc... with other things in it also.
It's not so much what else you need with it, I just tend to think unless all you plan to play is poorly produced basement Black Metal, ditch the pedal and invest in a decent rig.
If you turned up to a band audition for any kind of death or thrash metal band with just a Metal Zone as your primary source of gain, you are not going to be taken seriously especially if the band is a pro or even a semi professional band.
If you want my honest opinion, if I were auditioning guitarists and a guy walked in with an amp with just a clean channel and a Metal Zone for his primary source of gain, I'd tell him to come back with something that does sound like a box of bees or he just entirely doesn't get the gig.
A Metalzone does not produce good tone, period.
At the absolute least, if you can't afford to buy a new amp, buy a Line 6 POD X3 Live, or if that's too expensive, you can find an XT Live for around 200 US bucks these days and plug that into the front end of your amp. Sell your metalzone if you have to, to be able to afford a POD.
I have a POD X3 Live myself, and while it lacks a bit of dynamics compared to a good tube amp, for the price I paid for it and for what it is, it has very good tone and can cover a wide range of tones, not to mention it can sound great in recordings.
Your tone will improve dramatically.
If you're willing to spend even more and have the money, a good, decent priced amp on the used market like a Peavey 5150 will give you amazing tone for your dollars.
If you can get a Ibanez TS-7 Tubescreamer to add to it as a boost, you are very much in the ball park of what some pros are using.