I was considering a trade for 2 BTL 15s ( Single slug, spaceship motor), but the subs only have the cooling option. I am going from 4 SA-12s, and I like my lows. I'm powering them with 2 Audiopipe AP3ks. I was gonna run them in 3.5 per (7net), and tune between 30-33hz. I listen to alot of rap, low bass music, and I really want to be able to play in the high 20s/low 30s with authority. With just cooling, will these 15s be able to produce like I want them to? I'm only getting rid of the SAs to do a forward firing/sealed off setup, and I can't get 4 12s to fit in a blowthrough. I also wanted to see what FI was all about Thanks for any help