As I understand, 3C is stayman, 4N is quantitative, denying the shown major and offering to play slam in the other major or 6N. To begin a slam try and agreeing with 2N opener's major, I begin by bidding the other major since it is an idle bid. 2N - 3C 3H - 3S becomes a general slam try for hearts, and 2N - 3C 3S - 4H becomes a general slam try for spades. I don't know if this is good, bad, common, or anything, but I'm fairly certain that 2N - 3C - 3M - 4N is still quant.