Denon is known to work well with 4 ohm rated speakers despite what the manufacturer states as being rated at 6 or 8 ohms. If there is an impedance switch on the AVR leave it set to the highest setting. If this Denon unit has the features you want then buy it. Keep the unit well ventilated and you shouldn't run into any issues. For more indepth information, there is an article which relates to your exact question below.

http://www.audioholics.com/education/amplifier-technology/impedance-selector-switch-1

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