If you've got a multi-channel receiver and you want to connect one pair to the front right and left channels, and the other pair to the rear surrounds, then you should be fine. You're connecting each speaker to a different amplifier channel.
The only time you need to concern yourself with that impedance stuff us when you connect more than one speaker to the same amplifier channel. That's when that parallel impedance stuff comes into play.
It's nice to see you're paying attention, though. Your time here wasn't wasted. well...