you have a couple of options. you can install a mtx re-q or like i did, i install a infinity bass link attached behind the right 3rd row seat and i take the speaker wire as an input and sound really great. only proble is pass half volume, the head unit cuts the bass gradually, but enough bass to have an headache... i suggest also to replace the cheap speakers and you will have a new sound system. i replace bith front and rear for infinity kappas 6x8 component in the front ant co-ax in the rear and it sounds amazing.
