So how does one decide if an AVR can handle a particular speaker or not???
The best and most practical way is to listen to the AVR and speaker combo!
The theoritical way consists of comparing the AVR specs with the speaker specifications. Of importance are both the wattage of the AVR as well as the capability to drive low impedance loads (say 4 Ohm). This parameter is especially important if the speakers are of lower impedance.
Usually, the speaker specifications gives two impedance numbers, (1) Normal/Avg Impedance, (2) Min impedance. The AVR should be capable of handling the min impedance.
Also, speakers give a power rating range, say 40 W - 100 W. Then the AVR should be producing at least 40 W continuous power to drive the speaker sufficiently. To be on the safe side, the average power rating of the speaker (in this example around 70 W) can be taken as the thumbrule. Thus the AVR should produce atleast 70 W continuous power.
There are many more factors that effect what you hear - the size of the room, your listening distance from the speakers and the loudness levels at which you want to hear are all factors that can influence the selection of speaker-AVR combo.
Again, all this is theory, and can turn out wrong in the real world. The best bet is to listen.
Best,
APK