I have a V3i with 4 v-rated coils (4x6, 6x9, 10" DD and 300mm) and am considering the purchase of a used M6 as a back-up detector and/or loaner - I know that you can use some of the non v-rated coils on a V3i (with restrictions so to speak) but what about the reverse - can a V-rated coil be used on other Whites models?