It has been awhile since I've been involved in auto electronics. I have an extended cab Ford Ranger, factory head unit, and I have just installed four infinity 5x7's to replace he factory speakers. Next up will be an amp/sub combo. I do not know if I should run one 12" sub or two. I don't carry more than one other person in my truck all that often, but by the same token it is such a small space I don't want to overpower the 5x7's. I know I should probably buy a head unit but, I do like the factory cd player so I don't see the point in spending money on something I already have.