You are more likely to damage the speakers by driving the receiver hard, and into the condition Ian mentions. Your rec'vr will not deliver the rated power....it is simply not designed with the proper output stage or power supply to deliver the current required. By attempting to demand full volume from it, it will produce sever distortion....Worst case would be destruction of both output stage (I hesitate to say transitor stage, because most Japanese equipment is made from Integrated Circuits to meet price points in the market) and speaker damage.
The Onkyo you mention may be of more robust design, depending on the model. It may also be very similar.
BBIBH
