This is my proposed setup, some feedback would be great. The car does have rear speakers, but I clipped them long ago when I replaced the head unit and put the sub in.. The rears sucked and I don't feel are necessary to the setup.
I have nice eclipse door and dash speakers.. 5 1/4 and 3 1/2 respectively.. and a single 10" JL W2 sub in a box in the trunk.
The 4 channel amp is an eclipse, I really forget the stats on it, the mono amp is a jbl 300w... 150@4 ohms... the W2 10" sub is a 4 ohm speaker..
I'm so not an audio geek.. so hopefully we have provided all the necessary info.