That does seem to imply only stereo is supported, either limited by the laptop driver or the port you're connected to on the AVR, but I meant go to the Sound control panel. In System>Sound (one menu level up from your screenshot), if you scroll down, under Advanced, there should be a "More sound settings" that should bring up the Sound control panel, or you can search for "Control Panel", bring that up, and then click on Sound. Then right-click on the Denon-AVR device and select Properties. Look for an Advanced tab, where there should be an Exclusive Mode section with "Allow applications to take exclusive control of this device", and an Enhancements tab. But probably more important now, look at the Supported Formats tab and see what it shows for Max Number of Channels.