If the receiver doesn't have a 12v trigger, another alternative would be to use a power center with switched outlets. Some of them even offer delays or a programmed sequence where the power is applied to each outlet in order; ie the receiver is plugged into one of the outlets and the amp into another and when the power to the center is turned on it will turn on the receiver, delay a few seconds, and then turn on the amp.
The switched outlet on a typical receiver will say right next to it '120v, 1A max' which is definitely NOT for an amp.