Normally, I would choose one big sub vs multiple smaller ones. But in this case, as long as there’s freedom of placement, and especially considering this isn’t a question of one excellent sub vs 3 crappy ones, I’d go with three 2k’s. Without a refresher on the data, three 2k’s should offer nearly the same extension but offer more headroom, midbass performance, and the benefit of(potential) smoothing. Now, if you were asking about four 12” polks or Klipsch, I’d say buy the ultra(or 4k series) and save up for another right away. FWIW, I use three subs, and I think the 2,4,6,8 etc is just something people get stuck on. Not that there isn’t benefit, but no reason odd numbers can’t work.