The Pwr Amp takes over the heavy work for driving the Front L/R RP280FAs and the "Yammy" drives the remainder of the speakers. Like "Willand" said: "Headroom Baby!" My surrounds are RP280Fs and I'm seriously thinking about picking up another pair of the RP280FAs instead of the R260FAs for rear surrounds since they're both on sale; RP280FAs have a deeper discount than the R260FAs. Home Theater bug is much less expensive than car collecting, I can tell you that much, so I'm "going 'wit' it!" You can only live so many times with the time we have on earth :-)
I went with Emotiva's Basics line because the amp I have puts out 150W per channel, perfect for the RP280FAs and yes, I can hear the difference - not an instrumented test. The price was right so I simply had to experiment and "me likes." Just sounds more robust and then if you're into 2 channel stereo music, now you have a dedicated amp for those duties as well.
As I mentioned earlier, I am a novice and eventually - when the budget permits - I will step up to a true Pre/Pro & Pwr Amp separate set up but for now, just looking to finish off the 11.1.4 setup I have in mind, then add an extra Sub before settling down to watch the show! 11.2.4 - Almost There!