Firstly, this is a carPC forum. Unless you're installing a CarPC, this isn't really the place for you. You'd be better off finding a dedicated car audio forum.
If you have a four channel amp, and two sets of speakers (front component, rear 6x9), and your components come with crossovers, your option is this.
Connect the components to the crossovers, the crossovers to the amp. Connect the 6x9's to individual channels on the amplifier. You have four 'speakers' (as each crossover combines the components into an individual 'speaker') and a four channel amplifier. Therefore, one channel per speaker.