NikonShooter,
Those articles have all the relevant information for this discussion.
Impedance is not constant on a loudspeaker. It varies with frequency. So when you start to hook up two different models of speakers (even if they are the same brand) you will be mixing impedances at pretty much all frequencies. The rated impedance of a speaker by a manufacturer if its 4, 6 or 8 ohms means pretty much nothing.
To get an understanding how well a particular receiver will play with a speaker you would need to know the impedance and corresponding phase angle at each frequency. Speaker efficiency is another key factor, listening distance and SPL all matter too.
