I agree with PrsPlaya, that amp doesnt seem to have been built to make evry hi-gain sounds...You will need a pedal. If you go with an overdrive pedal, then you will use it at the same time as your amp is on its distortion channel, this means you can effectively have three stages: clean, amp drive, and off the wall drive from your amp and pedal.
You could also get a distortion pedal, from the sound you want, I think the Boss Metal Zone would be ideal(although the sound of this pedal is an aquired taste...and PrsPlaya seems to agree). Otherwise you could get a Boss Od20 twin pedal, which has about 20 different overdrive and distortion sounds, including the Metal Zone and maybe even an Mxr overdrive.
as for you amp, it sounds like you would want high,gain and presence to be almost full-up...it is not a guitar tone I like much, but that should get you a very "sharp" sound.
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