i would skip out on that and try to mod the stock subs the boss 8" will not sound right with stock 6.5" subs. if you run boss by itself it will not be as powerful as two 6.5".

i would read up and see the members who modded their stock sub bracket to house a bigger sub. then i would get a 150x2 channel amp and power the new subs with clean power and mount the amp behind the passenger seat towards the bottom of the floor where the net is and use a piece of 1/2" wood behind the carpet to mount the amp two. it will add around 15lbs since i figure the amp will be 8-10 lbs and the speakers will add an additional 3 lbs. this will be the best way to get some punch

i am going to be putting my focal subs up for sale soon and the bracket if you are interested. i was going to sell the subs and bracket separately since the bracket is modded to house a deep sub 3.03" deep speaker. i had it installed by a local shop and plan to go a different route for midbass in my system still tweaking it to my likings.