Need New System Advice, Selling Treo SSX

I curently have the following in my truck, and Im wanting to get away from the 18, love it to death, just want to be louder. 

JVC KD-AR7000, CDT EF-61 FG 6.5 inch components, powered by a Zapco Ref350

Treo SSX 18 in a 10.6 cu ft box tuned to 32 hz powered by AB VFL150.1 running at .5 ohms. 

Now, Im wanting to get away from the Treo 18, just too damn big and want more,.  thinking of gng for two 15's have about 12 or 13 cu ft to work with, might sell the amp to my buddy, and then get RF t20001bd to run the new subs.  My front stage is great, just want new beats.  Not looking for mainstream stuff per say, but won't not consider them.  Any ideas on what equipment to run with, I might be able to get another VFL150.1 and would just keep that instead of the RF.

Thanks in advance!

how much power is coming out of that amp?