You are a late comer to this thread. The issue was brought up earlier.
1. The DF and the speaker 8 Ohms values are ref. as resistive only (https://en.wikipedia.org/wiki/Damping_factor):
In an audio system, the damping factor gives the ratio of the rated impedance of the loudspeaker to the source impedance. Only the resistive part of the loudspeaker impedance is used. The amplifier output impedance is also assumed to be totally resistive.
2. This is not the reason speaker cables sound different!
There are as many attempts to explain, justify, point at factors without really checking it or study the matter. Impedance (as it is a complex "resistance" that includes an inductive (coil) and capacitive values, is none relevant when a speaker's cable (a good one) is way under 0.002 Ohms. For a cable, no matter how bad it is made (as a copper wire alone shall have no inductive or capacitance at all!) the values of those inductive (coil) and capacitive values are so low, that referred to the resistance value they have no effect.
Those values, with resistors of kilo Ohms do. This is a ratio of 1:1,000,000! Between 0.002 Ohms and 2k Ohms.