Uh oh! C'mon Sean, I'm not too sure about your explanation of this, and I'm tired. But the biggest issue re the problem with longer speaker cables is the fact that the amp sees them as part of the passive crossover network of your speakers! If there's even a small impedence change then the crossover will shift, resulting in a spectral coloration.
If you run XLRs you can run HUNDREDS of feet between a robust CDP and a great, transparent pre with NO issues. The recording pros do it all the time! I chose to run longer, asymmetric (yikes, eh?) XLRs between pre and monos, and shorter speaker cables. Glad I did. I'm forgetting some of the other reasons for this, but it also has to do with the source component's signal being voltage-driven, while the amp's issues in driving lines and crossover networks and drivers is a current thing, which is therefore more sensitive to cable length loading. Recording engineers ALWAYS run long mic cables to pres rather than long speaker cables. Can we get an engineer in here who hasn'y forgotten what he learned in a marijuana haze back in school in the 70's (me!)??