I have had Roon since February 2017. All of a sudden, yesterday (11/4/2017) Roon recognized my Marantz SR6006 on the network as an Airplay device (JRiver had already detected is as an DLNA device). I haven’t tried playing to it yet, I am just curious as to why it appeared so unexpectedly.
Don’t know the receiver in question - does it get firmware updates over the internet? Any chance it had an update recently?
It is an older unit (purchased 2011) but does get internet updates, I have not been prompted to install any recently.
My guess would be a firmware update to the Marantz AVR. Check it out and see if it works.
Roon music does indeed play on the Marantz SR6006.