grand prix

I recently bought a 1999 Pontiac Grand Prix Gtp. Before I bought it i had previously bought a pair of 6x8 and a pair of 6.5" kicker comp speakers. I looked online and it said stock my car has 5.25" in the front door panels and 6x9 in the rear, is there any way to fit my kicker comps into this...

Grand Prix chillin

Cleaned off the whip, shiny.

I want to know if it is possible to set up an aftermarket stereo on a Grand Prix without using the wiring harness adaptor (very expensive). I'm not afraid to cut wires so if that needs to be done then I'm all for it. I also don't care about the chimes or steering controls.