Shortly after posting this I experienced several housewide brownouts and a series of short power failures, so I'm guessing the cause of my initial problem is some unstable electricity.
I can also hear my computers UPS clicking on and off into saftey mode even as I type this (though I'm not seeing any other signs of brownouts, but obviously there's some instability going on).
My home theater is all connected through a power center/battery backup, so my guess what happened here is, the electricity right now is unstable, and turning on my system was too much of a draw temporarily (even for the battery with low in-voltage) given that, so the receiver probably clicked into some sort of protection mode to protect itself. At least, that's what I hope happened.
At any rate, the smell I smelled wasn't what I'd classify as a "bad" smell (could have even been the power center instead), and everything with the receiver is working perfectly, so hopefully all is functioning normally and the thing just reacted to the wonky power situation here, which explains why I've used it for weeks without experiencing anything like this. =)