wyliec2,
Most AVR's, or stereo receivers, feature a simple 12v regulator circuit, capable of around 50ma of available current. What you related from the R2150 manual, was the description from the rear panel(RP5) illustration. A more complete summation is found on page 16 of the manual:

"The RR 2150 has one 12 volt Trigger output that output offers a 12 volt DC
signal that can be used to control compatible external components such as
amplifiers, blinds and projection screens.
To control an external device such as an Outlaw power amplifier with the RR
2150, connect the Trigger Output (RP5) on the rear panel to the matching
“Trigger” or “Control” input on the external component.
Once the two units are connected, the external component will turn on when
the RR 2150 is on, and off when the RR 2150 is turned off."

Kubrickfan, there are devices such as current sensing power strips on the market that range in pricing. I have not used one, but, maybe someone on the forum can recommend one.