M&K push-pull config???? suggestions?

i've heard good things about m&k's mx line of subs with the push-pull 12"'s, but have not actually listened for myself as the dealer closest to me just got rid of m&k. they even have the push-pulll 8" model mx-70B out now. those of you that have listened to these by miller and kreisel, please enlighten me on their benefits as compared to going, say, with one of their single 8" or 12". any help would be greatly appreciated!