Surround sound, cheap and easy?

I stumbled upon this the other day: http://electronics.howstuffworks.com/surround-sound7.htm Seeing how easily you can create a matrix surround system using a two-channel home amplifier makes me interested in applying this in a vehicle. My only concern about this kind of setup is what kind of impedance a two-channel car amp would see when using 4-ohm speakers (since most car speakers are rated at this)? I only know the basics of Ohm's law, so I'm somewhat stumped... Assuming it doesn't create too low of a resistance rating for any affordable stereo amp to handle, I'd like to give surround sound in the car a try. I figure that this kind of setup would create a much more realistic sound stage, as compared using the common methods of adjusting for rear fill.