pioneer sat nav + speakers and sub

[samp4856]

right basically if i do get a mazda 2 next year then i will be getting the pioneer sound systym as my mazda 3 has bose atm and i will miss the BOOM BOOM BOOM will.i.am talks so fondly of, but along with it i will also be upgrading all the door speakers to 3 way pioneer one and i will also be placing a underseat pioneer subwoofer in there aswell, but i have seen on scotts tamura he has placed 6 by 9's in the parcle shelf, so im asking wether the pioneer head unit can hold 6 speakers as aaposed to the normal 4 or wether or not he has spliced the old speaker wires, or disconnected the rear ones all together in order to have the new ones in!

many thanks sam!