92 caddy audio upgrade

I just bought a 92 cadillac STS with the bose system in it, and I want to upgrade it. the problem is, as I have read online, you can't change the individual componants, you have to replace the whole system. I do have a mostly complete stereo from my other car, but the front door speakers look to be three inch, I want to do 6 1/2's. Any suggestions? Does anyone know if kick pods are available for it?

you can either make mounts to fit them in the door or look for some prefab kick panels. Kinda hard to believe a door speaker would be 3" ..... those usually go in the dash.