I can’t get the Phantom to throw back changes to it’s volume when I change it via Spark. It means if you use your knob, Roon will get out of sync with the volume 
The “beta” UPnP doesn’t seem to do subscriptions properly. Shocking. I hate UPnP.
@mvrlogins, is that your experience too? If you change the volume in Spark or with the knob, does Homebridge get the events?
I have a Nuimo Control… it’s a really nice knob. Let me see if I can get that working… I didn’t think about it since I’m trying to get them to open up an API for their hub, but I bet I can do something hubless because I have an RP with BLE support.