OK I've confirmed the uneven speaker counts were causing this hum. I will run the trueRTA measurements and post them in the coming days but I will also try the various pinout/cable arrangements suggested by JC and Tom and also post trueRTA results cross referenced and matrixed.. though I don't have the gear to measure accurately on the highend of the spectra. It looks like my uncle is gunna just have to order a rear center and a couple of Algonquins to solve this issue ;\) Lucky guy...