I've owned and operated a V3i since 2010. I got an M6 a couple years as a backup and like you, my M6 finds coins better than the V3i on most days. I once asked if the V3i could be made to exactly run like the M6 and the answer was, "Why would you want to limit the V3i?" or something like that. I still run the V3i after all this time but I can guarantee you that the M6 will kinda run circles around the V in clad count where I've come home light in the treasure pouch.
I truly hope that you find an answer for us. I'm not saying that I haven't found some great stuff but I will say that I have never matched the top two tectors on group hunts as far as clad/coins after hunts. what disses me is when they follow me over a spot and dig coins I had just missed. Either I am a terrible tector, or I've never mastered the settings, or the V3i won't ever work as efficiently as class-B detector models.
Some will surely ask, "Why don't you lose the V3i and move on." That's a good question. The V3i is supposed to way better and I paid for it to be. My vendetta is to keep hammering on it.