Hi
It all depends on your budget and what all features you want in the 5.1 / 7.1 AVR or stereo amp....
If you want to connect all your digital components (CD player/Set top Box / X Box etc) to it then AVR is the answer.....else stereo integrated amp.
Depending on your budget and the specs of the speakers, go for the avr /amp which can output continous 75% watts of the speaker watts...(see the ohms load factor too)
Audition and decide