I bought the GT-8 a few months ago and I'm impressed overall by it. But the thing that really annoys me about is the amp models and pedal models for all the metal ones are terrible and sound nothing like the original. I'm finding incredibly difficult to get a good metal tone out of it. The other a friend of mine leant me the metal zone stomp box and I found a couple of good tones out of that. But I can't get it out of the GT-8. Could someone who has it help me out and maybe direct me to the way of finding a decent metal tone, preferably something a little bass heavy with the GT-8?
The Metal Zone is yuck, the Metal Core is a much better pedal for metal tones. That and the EHX Metal Muff would be the best 2 IMO.

As far as your GT8 goes... maybe fiddle with the EQ? One of my mates at school had one and we managed to get a pretty good metal tone out of it, but buggered if I can remember how, he was running it through a cheapo 20W practice amp.
Well I mean I could get something I liked out of the metal zone on the stomp box but not when i was using the model of the metal zone on the GT-8.

I've tried that as well but I just can't seem to get anything decent. Even the preset patches dont sound great.
Well gt8 is not best at metal tones. So try the metal stack amp model bass treb at 7-8 mids at 2-4 gain 80-90 maybe add some compressor try it.