Looking at the back of your avr, it doesn't have pre-outs. The zone b is labeled as a line out, which means it won't provide volume control (unless there's something you can set in the avr itself to toggle that to a pre-out as some can do, but yours doesn't appear to have the capability). Would this be just for 2ch use? An external amp's wattage is what it is....and difference between your avr and the external amp isn't particularly significant (about 2dB), altho perhaps could improve on impedance handling capability. However, you'll need a different avr if you want to use an external amp.. If you want to use the power amp as part of a multich setup, just best to have an avr with a full set of pre-outs (i.e. for all channels).
Now, if you want to use your zone b with your power amp, you'll need a pre-amp to control volume.