Hey Nick,
I have stock 17's and with 4 people in the car I have spun out from a light trying to accelerate. The sub-box isn't going to make THAT much of a difference, but take it out and see what happens.
The ECU upgrade I am talking about though is one you can get from SRT. I don't know if they sell just the piggy-back ECU by itself or only with the Intake upgrade. Apparently, from the research I have done, without the piggy-back ECU an intake upgrade is like throwing money out the window.
Give SRT a call and see what they can do for you.
SRT - Swift Racing Technologies