Getting ready to purchase the V3i and heard mixed reviews about the stock coil. I don't like the bigger coils but would like to by a smaller one. I would like to buy the concentric coil... but does it work with the 3 frequenceys? Do any of the coils have to be tuned to the machine? Any thoughts on the 5.3 (6x6) coil and depth? I know this has been asked before....wonder if there is any new info? Thanks...