If your denon had to dish out 650W a side into 4 Ohms from 20Hz on up, it would turn into puddly goo. At 90% efficiency and at that level, the ADA is still turning about 150W into heat. That's like 3/4 of the power of your Denon. LOL.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated