The benefit of multiple amps depends on how much is power is demanded by the speakers and how loud you play them. Its easy to clip amps momentarily during loud passages. While not as dramatic an effect, there was a time when small subs were also powered directly by HT receivers. Now most subs come with their own amps which take the load off the main receiver-amp when you cross to the sub amp. In effect directing a separate amp to the surrounds accomplishes the same thing.
I'm not suggesting anyone go off and buy an identical receiver, but seeing how he has one it makes sense to put it to good use. I know some people who have three amps going: one for the centre, another for mains and a third for surrounds. With good quality speakers the difference is audible, especially if you play movie soundtracks loud like I do.
