Unfortunately, some chromecast devices (as speakers) wont work using BubbleUPnP. Can configure everything, but wont play. I have some chromecast III connected to tvs that work just fine, and some chromecast speakers that dont...
Does the Google Home app on your phone cast to your chromecast speakers ok? If so, you can have JRemote2/BubbleUPnP send a DLNA stream to your phone, then try Google Home on your phone to cast to speakers. A clumsy work around, but it did succeed with my Chromecast Audio dongle in a test. Playback was still controlled by JRemote2.
Another option to try (which also works nicely for my Chromecast Audio dongles):
1) Use latest BubbleUPnP Android app as your remote music player instead of JRemote2. Select JRiver MC server as its library and then More > Select Renderer to choose speakers.
2) Set up JR MC to serve your desired views through its Options > Media Network > Add or configure DLNA Servers ... > Generic DLNA > Customize views...
3) Use Google Home Android app to verify what's playing and confirm volume level.
If nothing works, try support at
https://bubblesoftapps.com/bubbleupnpserver2/docs/support.html.
