Until Marantz AVR range are certified Roon Ready then HDMI or using Airplay or the extension RHEOS are you only options. Roon uses its own streaing protocol as well as supporting a few others such as Airplay, Chromecast, Sonos, KEF and Linns Songcast but it doesnt support HEOS or UPnP. Marantz and Denon have added Roon Ready code to HEOS in a lot of their 2 channel kit but as yet nothing for their receivers.
If you where looking for multichannel playback then that will not work over network at all only via HDMI as HEOS architecture doesnt support it with or without Roon Ready status.
Have a look at RHEOS as a solution but it does require some setup if your using Windows/MacOS. I used it for 18 months until my Model 40n became Roon Ready earlier this month.