“The 13-channel decoding in the AVR-X8500H can be configured in either 9.1.4 or 7.1.6 layouts. The 9.1.4 option returns use of Front Wide speakers, which Denon had stopped supporting for a couple years to some owners’ dismay. Be advised that, in Dolby Atmos, only sounds specifically encoded as objects will pass through the Front Wide channels, and the Dolby Surround Upmixer ignores them altogether. DTS:X and the DTS Neural:X up-mixer may put those speakers to more use.
If Front Wides are not of interest to you, the two additional channels can be used for height speakers instead. Previous mass-market receivers were limited to four height channels of sound, the most typical arrangement for which was Top Front and Top Rear designations. In most rooms, that should be enough to provide strong height effects with separation and directionality. When an airplane or helicopter is supposed to fly overhead, you can hear it move from the front to the back of the room or vice versa. On the other hand, four channels may not be enough for particularly large rooms or those with challenging physical limitations. My own home theater has a low ceiling which, when combined with the distance between Top Front and Top Rear speakers, left me with an auditory hole above my head. Adding two more speakers in Top Middle positions helps to anchor sounds where they did not image adequately before.