Agree the best simple way to know if your stuff wastes power at idle is the see how much heat it puts out when idling. Nearly all the electricity used at idle is going into heat. The warmer the stuff is at idle, the more electricity you are using at idle.
My prior amp (forte 4a) was a small furnace at idle, and was just as hot idling all day as it was playing hard all day, Class "A".
My current amp, a Bryston 4B-SST2 has more surface and less apparent heat output per square inch, but it is much bigger and twice as heavy as the Forte.. so it is hard to say if it is more efficient?