If it was me I would get the boxes for the 6X9's and put them under the seat. If you still have a bench seat you can build boxes and put 10's in there and go with the 6X's. The only thing is you need to know the watt's the speakers will hold before putting in amps and all. The head unit my put out enough power for what you want. It just depends on how loud you want the system.
James