"I notice the 5740 doesn't have multi-zone capability. Were you just tacking on more speakers in parallel, thereby lowering the impedance?"
Yes. As near as I can tell the Yamaha doesn't like the lower resistance. Now the HK 3480 has plenty of power, but (as mentioned above) doesn't sound as good. The music just doesn't have that "I can almost see the musicians in front of me" sound that came out of the M22s before the receiver change. They now sound only slightly better than the speakers in the other 2 zones which I chose largely for their lack of cost (e.g. $49 for a pair of outdoor speakers).
