I have an older Yamaha (RX-V1070) that sucks for H/T - and it shouldn't as it was one of the top of the line Receivers. Whenever a huge, loud explosion happens, the POS would die off (very little sound). When it came time to upgrade I got an H/K 520 and haven't looked back. It is rated for 75 watts/channel, 5 channels driven. But as JohnnyG said, the ratings are not very accurate. For instance, the Yamaha states that it is 6x90watts - so what (no pun intended) as those measurements are usually measured ONE CHANNEL DRIVEN - i.e. if all 6 channels are being driven at the same time, the wattage drops considerably (probably in half) whereas HK measures ALL CHANNELS DRIVEN - so when they say 45watts, they mean it. For instance, when I drive only two channels, the H/K is rated at 90 watts (not 75).
I would stay away from Yamaha, and go with the H/K in a heartbeat. My H/K easily drives my speakers and NEVER loses volume in any explosions - I'll never buy Yamaha again!!