Drivers with a pro audio lean do not work in a 2 way. Period. Zero exceptions. Efficiency and wide frequency response do not go hand in hand.
Would be better to make a thread than to ask in a thread from 16, but kudos to you for searching first instead of just asking the same question that gets asked over and over again...all because of some misinformation elsewhere in the mobile audio world.
That being said, first step is to understand your goals and to reset them. There is no 2 way that will play to 100hz at the level your SA-12 can. Not even close. Of course if you had that as a set you probably wouldn't love it anyways. Next step is to understand what you have for processing, background and what all you are contemplating to help the overall installation. Experience you have with anything and like/dislike would also help.