I'd done this before back in the day when I was first setting up my dedicated theater. I forgot I used light gauge wires to my surrounds to make sure everything worked and sounded good where they were set up. I got caught up doing some louder than usual listening and the receiver went into protect mode, just like you described (oops

). Once I remembered about the wiring and replaced it as I initially planned, it was good to go w/out cutting out again.
I will say though, that once I had the opportunity to try running with external amplification, even with just my mains taken off the receiver's internal amps, I was hooked and haven't looked back since in my dedicated theater.
There's lots of solutions, inexpensive and reliable to esoteric and artsy-fartsy amps to choose from. If you're just looking for some extra kick for your mains, something as simple as a Behringer A500 to power your mains would give you some extra headroom for as little as $200. If you've got a bigger budget, you can get a bit more power or even a multi-channel amp if you'd prefer, though the front L/C/R are going to handle the majority of the load, so a two or three channel amp should give you the added headroom you need/want w/out spending an arm and a leg... -TD