Sensitive or efficient?
if sensitive then I would suggest a pro audio driver. TH or FLH or simple ported all work well.
So what space are we working with to start?
If the columns up front then that is a tuff space for a single ported 12 because your using a sono tube. If building yours with MDF then going with a bunch of cheap 12's would work. Like a line array if you will. Maybe four per side. But your looking at maybe 92-94db sensitivity.
For hitting down low(20hz) you will need a lot of volume. Mainly because you have a large room. So when going with that direction you need about a pair of 18's to start. Then go from there. So just building the sono subs limits your spl. You could go up and down firing pair of 12's in a sono tube but this will be likely a sealed cabinet. So that means 20-30hz wil probably be not as loud as the single ported cabinet. BUT everything else would be louder.
I dont want to talk you out of any design you may have your heart set after. BUT line array style four 12's per side would be pretty nice to go along with K402's. The 12's can be ported or sealed and can be whatever car audio so long as you have T/S parameters. If and when you have a possible driver to choose I cab model for you. I will be home the next few days so I can model.