Ok this is what I did,
Go and find you some 91-92 door pannels with the 6.5" speaker mounts in them, put some components in there and put a 2 channel amp to them and forget about the rears. I tried several things and ended up giving up on it. The exhaust is loud and the rears you never hear. I also have a 10 inch Type R sub, 10 is plenty in a supra, with little effort