honestly it looks like this or a device like it is the best solution http://www.rockfordfosgate.com/products/details/dsr1when it comes out soon
uses the line level from the head unit and communicates with canbus to figure out the volume and fade and such
no center but who cares? extra speakers are a gimmick. in my old car i had only two woofer/tweeter component sets in the front and a sub in the back. the key was really the 150w RMS per channel to the front, not the number of speakers.