After your last comment, I would agree with Gonk. It sure sounds to me like you are running low ohm loads through the receivers you have tested and thats why they are cutting out.

Most "cheaper" recievers are not really designed for such low impedence loads and its not uncommon to experience what you are seeing.

I don't think there are any Outlaw amps that are not designed to run at 4 ohms. Except maybe the 1050, which is discontinued.