Cello-
The problem w/reefers as a burn-in tool is, as you noted, they are primarily off (unless one believes the light stays on.) This is increasingly the case the newer they are, and more so if they are an EnergyStar model. It also depends on much the door is opened.
The upside is that you don't waste electricity.
The downside is, for my reefer, it takes a full 24 hours to run a dinky 500W through it; an average of 28W per hour. This is hardly a "burn-in". I can accomplish this in 20 minutes on the microwave oven; a 100W floor lamp for an evening; a couple of washer loads.
But really, after a day of this fiddling, I'm of the mind to use the power amp as the burner for a few days, quit being anal/obssesive, and listen to some tunes. A PC doesn't carry music; just a one-note drone tone...