I know this isn't very helpful, but one day while playing around on the G5n, I stuck the DIST 1 in front of one of the Marshall amp sims (sorry can't remember which one) and it sounded almost exactly like the tone from Grinder. I should have saved it but it was so simple I didn't think to. Anyway I'm not in front of my unit now, but hopefully that gives you somewhere to start. Good luck.