Hey there dude i have a RMC preety nifty little things aint they! Any way As to your q's i would suggest putting it on the R-Fier Setting, put the Tone on about half(about 12), the Gain on at about 3 O'Clock, Volume is up to you but adjust the other setting saccordingly. I put it at about 9 O'Clock. I prefer a thicker tone than this but this should do you quite well for a metallica.
Rock on dude!!!