SPL is correct about the frequencies that you are trying to "enhance". Finding the proper phasing in our vehicles has always been a challenge. I struggled with this for most of my first season of competition.
Once JL Audio worked with my car at the 2001 IASCA World Finals, we changed some crossover points and the phasing of the passenger woofer and I scored the 3rd highest sound quality score.
Wiring the vehicle as I have described will give you fantastic imaging for the drivers seat. In order to get proper imaging and staging for both seats, you will have to do kick panels.
