Don't get a big muff man, bad advise.
The other guys gave you the best hints, it's different for every setup, but you need to have a play around with your EQ and tone settings.
When i got my JMP-1, i sat there and thought "right, i can just about get whatever Marshall sound i want out of this thing, what do i want?" and for the next day, all i did was listen to guitarist's tones that i liked and tweaked the EQ's until i had a dozen different clean and dirty channels in different stages and went from there.
If your chugga chugga powerchording setting is good but the leads suck on it, then most probably it is your ears that are fooling you into maxing the rhythm sound to maximum chug, and your leads are suffering. Try setting it the other way around, set up your tone so that your leads sound sweet, and then tweak (very slightly) to get the rhythm sound. If you turn your amp on and play on the highest gain setting and then turn it down, it will always sound lower in everything and suck, but in reality, if you turned your amp on and it was set lower, the only person who would know that it wasn't at "maximum warp chug" would be yourself.
Just something to think about.
