JohnK and SirQuack are on the money on this one. It's the first report I've heard of Outlaws shutting down, so I'm fairly sure it's a ventilation problem or perhaps an intermittent short in the speaker wire connections.
On the other hand, the M80s will handle huge amounts of clean power and I have had personal experience at an Axiom party of two of five 350-watt monoblocs shutting down at what I consider were absurdly loud levels. (I was wearing ear plugs and was out on the deck. .)
If you find that ventilation or speaker wire shorts aren't at issue in your system, I'd consider other brands besides Emotiva, since some models of those have had shut-down problems. Look at Parasound, Anthem, and Bryston as well.
Also, regarding the "0-dB" level on your preamp, depending on the voltage output of your preamp at that level, it's quite possible you were already overdriving the Outlaws into clipping, which would shut them down.
Axiom Resident Expert