The projector is not a source. It does not support audio only through HDMI (this isn't actually a thing anyway). It does not support audio return channel. If it did, it would be listed on the specifications or labeled right on the back of the projector.
View specifications of HT3550, BenQ 4K HDR Home Theater Projector with 95% DCI-P3
www.benq.com
Since you are already hooking up your receiver to a TV in the room using the ARC connection, then that would be used to playback from smart functions built into the TV.
At the projector, even if it had something built in, you wouldn't want to use it. Instead, just use a smart appliance which has the features you want. Like Roku, GoogleTV, Chromecast, AppleTV, etc. Then plug that smart device into your Marantz as another source for your system.
The ONLY connection you make between the Marantz and the projector is the HDMI OUT 2 connection. That will feed video from your source, through the Marantz, to the projector. The projector will act like a computer monitor. It won't be a source or smart device in any way whatsoever.
manuals.marantz.com