As for creating something that resembles grouping: I've settled on using the Set Track feature, pointing the player to another one that's already playing what I want in the group, using it from Rule Machine. Note that this does not use node-sonos-http-api.
In my case,
Living Room Sonos: Set Track: x-rincon:RINCON_78XXXXXXXXXX01400
The RINCON_78XXXXXXXXXX01400 number is device UDN. You can get this by inserting the MAC address of the source device (i.e., the device whose audio you want to take over) into RINCON_<MAC-ADDRESS>01400.
