If you want some bass coming out of a 6" driver you'll need a very good brand, I just don't think Pioneer is up to the task, I would use something along the lines of Focal, Image Dynamics or MB Quart.

Thos brands have 6" mid-bass drivers, but don't expect much from them, in this particular casi, size does matter.

My car is being finished as we speak, I'll post some pictures later, I installed a 12" sub and did not loose that much space in the trunk.