Before doing any reconstruction, try some troubleshooting first.
First. make dang sure you don't have any hairline shorts in your speaker wire splices. That's why I like to stagger my splices by about two inches or so, to assure there is no possibility of a short.
Second, take the receiver out of the cabinet and play it normally for a few days just to make sure it's not a receiver problem. I'm sure the SO will allow this for an experiment to isolate the problem, won't she?
If it still kicks off outside the cabinet, you know there's either an issue with the receiver. You may be asking too much from it, it may not like load the speakers present, or there's a problem with the receiver itself. First things first. See what happens.
If it works fine outside of the cabinet, try that fan suggestion from rickster but remember, the receiver is designed to draw in cool air from the bottom and sides and pass the heated air out the top.