Agreed. Don't limit yourself to a 5.1 receiver. They actually have much smaller power supplies and will perform less. It's the size of the main power supply / transformer that matters. example:
Yamaha 2070 - 9 channels - 37.5 lbs
Yamaha 1070 - 7 channels - 32.8 lbs
Anthem MRX 520 - 5 channels - 28.2 lbs
The Anthem is the best 5 channel. It might have better components internally, but it will not be able to compete in brute force power. The larger transformers and power supplies of the Yamahas will be able to provide stronger bass/midbass, even at lower volumes!
Also, none of these receivers will be able to match a dedicated 5-channel amplifier, which can get into the 60-90 lbs area.