I will test this with my resistor load I built and see. There is the benefit of reactive load from a correct set of speakers here and a power load added, minus subjective reactive load technique with makeshift inductors plus you skip over anything a reostat may introduce in theory

Won't take more than soldering in a 1/4" jack. I will try and report back as soon as I get time.
My thinking is if you ran 4 4x12's off one speaker jack and those 4x12's were wired series parallel to get back to 16ohms load total and 3 of those were silent then it would have to bog some stuff down someplace. I will check it out.
that would make with my resistors a 400watt total load. 300 being extra. Theoretically you could potentially create a 1300watt total load if you wired 12 resistors/motors and 1 4x12 this way.