hey guys what is a great sounding proffesional preamp.i am looking for killer gain(old metallica style)with a full lead sound and great tone.i am thinking of just going to a rack system as i am tired of the limited tones i get with my stack.i have tried randall,marshall,crate,mesa boogie,and more(heads i mean)and i just can't get what i'm looking for.maybe if i run a processor through my marshall?i am an old style metal guitarist and i am just not familiar with the sound aspect.