You can use the Denon but make sure any sound processing is turned off. Use the Marantz as the sound processor. Keep in mind that the gain of the Denon, Sunfire and Marantz may all differ which will affect the ultimate SPL you can achieve. This may be more of a theoretical rather than a practical concern for you.

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