Sir get the W3002D2, just kidding.
You have a good AMP, I do not know why you want to go SPL, if I were you I would have choose the JBL P1222.
However for SPL you can go for 2 X Kenwood X1224, I have listened to them in a friend's Lancer, they are good and underrated, they might fit in your budget, you can give them much more power in future.
If you do not have space for 2 SUBs you can also have a look at CV VMAX 15" if its available in your budget for a little respectable sound else the Kicker L5 can really go loud.
For low budget a traditional Kenwood 2 X 3012 or 308D4 will do the job, I like the 3012 more, if you can sacrifice some loudness for lyrics GT5 12 are much better and they can use power more efficiently even in poorly designed enclosures (the ones in those American boxes PW member has showed are really good looking and well built).
Everything depends on your enclosure and how much electric power your car can fed to your AMP.
Regards
