I have a 2002 pontiac bonneville, i have a FI BTL 18 right now, running of of an audiopipe aqx 3500. I ordered a ZCON 18 a few weeks ago and haven't built a box for it yet. The most i can get out of a box is around 6.5 cubes. Any idea which one will be better to go with? also, it's mainly for music thanks