any opinions on a better upgrade

[akabosco]

ive got an alpine 1243 type x and an alpine amp and it's just not loud enough. i want to go big. after a lot of shopping around i priced out a dd 9512i sub and dd m3b amp for an upgrade here in a bit. i just wanted to hear some opinions anyone has on anything that would have better sq with a lot of spl. i have a trunk car and may not be able to fit a 15 according to the dd sales rep but i think i have a relatively big trunk in my 05 kia amanti. i don't want to spend more than 2000 maybe up to 2500 on the sub/amp/power cell. would two 3500's better/louder and what amp would you use for that? (lanzar?) is there an amp out there that is better suited for the 9512i? i don't live near any dc dealers so i cant do them.

thanks for taking the time to help me look into this