It's snake oil, and it won't work.

Power tube saturation doesn't occur when you just turn up the master volume; the tubes have to actually be outputing at a saturated level. The only way to get them to be saturated, but not have huge volume, is to attenuate the power after the power amp, before the speakers. Or stick the speakers into a sealed box.

His comment that a power soak will shorten the life of the tubes is also bunk. The tubes will only have a shorter life if you run them harder as a result of having the soak in there.